feat(ui): full-screen artwork viewer for album cover art

Sources/Kaset/Resources/ar.lproj/Localizable.strings

@@ -566,3 +566,7 @@
 "Start a new chat to continue." = "ابدأ محادثة جديدة للمتابعة.";
 "Ask Gemini response ready" = "رد «اسأل Gemini» جاهز";
 "New Ask Gemini chat ready" = "محادثة «اسأل Gemini» الجديدة جاهزة";
+"View Artwork" = "عرض الأعمال الفنية";
+"Album Artwork" = "أعمال الألبوم الفنية";
+"Artwork Unavailable" = "العمل الفني غير متوفر";
+"This track has no artwork available." = "لا يتوفر عمل فني لهذا المقطع.";

Sources/Kaset/Resources/de.lproj/Localizable.strings

@@ -566,3 +566,7 @@
 "Start a new chat to continue." = "Starte einen neuen Chat, um fortzufahren.";
 "Ask Gemini response ready" = "Antwort von „Gemini fragen“ ist bereit";
 "New Ask Gemini chat ready" = "Neuer Chat mit „Gemini fragen“ ist bereit";
+"View Artwork" = "Artwork anzeigen";
+"Album Artwork" = "Album-Artwork";
+"Artwork Unavailable" = "Artwork nicht verfügbar";
+"This track has no artwork available." = "Für diesen Titel ist kein Artwork verfügbar.";

Sources/Kaset/Resources/en.lproj/Localizable.strings

@@ -35,3 +35,7 @@
 "Start a new chat to continue." = "Start a new chat to continue.";
 "Ask Gemini response ready" = "Ask Gemini response ready";
 "New Ask Gemini chat ready" = "New Ask Gemini chat ready";
+"View Artwork" = "View Artwork";
+"Album Artwork" = "Album Artwork";
+"Artwork Unavailable" = "Artwork Unavailable";
+"This track has no artwork available." = "This track has no artwork available.";

Sources/Kaset/Resources/es.lproj/Localizable.strings

@@ -566,3 +566,7 @@
 "Start a new chat to continue." = "Inicia una nueva conversación para continuar.";
 "Ask Gemini response ready" = "Respuesta de Preguntar a Gemini lista";
 "New Ask Gemini chat ready" = "Nueva conversación de Preguntar a Gemini lista";
+"View Artwork" = "Ver arte";
+"Album Artwork" = "Arte del álbum";
+"Artwork Unavailable" = "Arte no disponible";
+"This track has no artwork available." = "Esta pista no tiene arte disponible.";

Sources/Kaset/Resources/fr.lproj/Localizable.strings

@@ -566,3 +566,7 @@
 "Start a new chat to continue." = "Commencez une nouvelle conversation pour continuer.";
 "Ask Gemini response ready" = "Réponse de Demander à Gemini prête";
 "New Ask Gemini chat ready" = "La nouvelle conversation « Demander à Gemini » est prête";
+"View Artwork" = "Voir l'art";
+"Album Artwork" = "Pochette de l'album";
+"Artwork Unavailable" = "Pochette indisponible";
+"This track has no artwork available." = "Aucune pochette n'est disponible pour ce titre.";

Sources/Kaset/Resources/id.lproj/Localizable.strings

@@ -566,3 +566,7 @@
 "Start a new chat to continue." = "Mulai chat baru untuk melanjutkan.";
 "Ask Gemini response ready" = "Respons Tanya Gemini siap";
 "New Ask Gemini chat ready" = "Chat Tanya Gemini baru siap";
+"View Artwork" = "Lihat Karya Seni";
+"Album Artwork" = "Karya Seni Album";
+"Artwork Unavailable" = "Karya Seni Tidak Tersedia";
+"This track has no artwork available." = "Lagu ini tidak memiliki karya seni yang tersedia.";

Sources/Kaset/Resources/it.lproj/Localizable.strings

@@ -566,3 +566,7 @@
 "Start a new chat to continue." = "Avvia una nuova chat per continuare.";
 "Ask Gemini response ready" = "Risposta di Chiedi a Gemini pronta";
 "New Ask Gemini chat ready" = "Nuova chat di Chiedi a Gemini pronta";
+"View Artwork" = "Mostra copertina";
+"Album Artwork" = "Copertina album";
+"Artwork Unavailable" = "Copertina non disponibile";
+"This track has no artwork available." = "Questo brano non ha una copertina disponibile.";

Sources/Kaset/Resources/ko.lproj/Localizable.strings

@@ -566,3 +566,7 @@
 "Start a new chat to continue." = "계속하려면 새 채팅을 시작하세요.";
 "Ask Gemini response ready" = "Gemini에게 질문 응답 준비됨";
 "New Ask Gemini chat ready" = "새 Gemini 채팅이 준비되었습니다";
+"View Artwork" = "아트워크 보기";
+"Album Artwork" = "앨범 아트워크";
+"Artwork Unavailable" = "아트워크를 사용할 수 없음";
+"This track has no artwork available." = "이 트랙에는 사용할 수 있는 아트워크가 없습니다.";

Sources/Kaset/Resources/nl.lproj/Localizable.strings

@@ -566,3 +566,7 @@
 "Start a new chat to continue." = "Start een nieuwe chat om door te gaan.";
 "Ask Gemini response ready" = "Antwoord van Vraag Gemini is klaar";
 "New Ask Gemini chat ready" = "Nieuwe chat met Vraag Gemini is klaar";
+"View Artwork" = "Artwork bekijken";
+"Album Artwork" = "Album-artwork";
+"Artwork Unavailable" = "Artwork niet beschikbaar";
+"This track has no artwork available." = "Voor dit nummer is geen artwork beschikbaar.";

Sources/Kaset/Resources/pl.lproj/Localizable.strings

@@ -566,3 +566,7 @@
 "Start a new chat to continue." = "Rozpocznij nowy czat, aby kontynuować.";
 "Ask Gemini response ready" = "Odpowiedź Zapytaj Gemini jest gotowa";
 "New Ask Gemini chat ready" = "Nowy czat Zapytaj Gemini jest gotowy";
+"View Artwork" = "Pokaż okładkę";
+"Album Artwork" = "Okładka albumu";
+"Artwork Unavailable" = "Okładka niedostępna";
+"This track has no artwork available." = "Ten utwór nie ma dostępnej okładki.";

Sources/Kaset/Resources/pt.lproj/Localizable.strings

@@ -566,3 +566,7 @@
 "Start a new chat to continue." = "Inicie uma nova conversa para continuar.";
 "Ask Gemini response ready" = "Resposta do Perguntar ao Gemini pronta";
 "New Ask Gemini chat ready" = "Nova conversa com o Gemini pronta";
+"View Artwork" = "Ver arte";
+"Album Artwork" = "Arte do álbum";
+"Artwork Unavailable" = "Arte indisponível";
+"This track has no artwork available." = "Esta faixa não tem arte disponível.";

Sources/Kaset/Resources/ru.lproj/Localizable.strings

@@ -566,3 +566,7 @@
 "Start a new chat to continue." = "Начните новый чат, чтобы продолжить.";
 "Ask Gemini response ready" = "Ответ «Спросить Gemini» готов";
 "New Ask Gemini chat ready" = "Новый чат «Спросить Gemini» готов";
+"View Artwork" = "Просмотреть обложку";
+"Album Artwork" = "Обложка альбома";
+"Artwork Unavailable" = "Обложка недоступна";
+"This track has no artwork available." = "Для этого трека нет обложки.";

Sources/Kaset/Resources/sv.lproj/Localizable.strings

@@ -566,3 +566,7 @@
 "Start a new chat to continue." = "Starta en ny chatt för att fortsätta.";
 "Ask Gemini response ready" = "Svaret från Fråga Gemini är klart";
 "New Ask Gemini chat ready" = "Ny Fråga Gemini-chatt är klar";
+"View Artwork" = "Visa omslag";
+"Album Artwork" = "Albumomslag";
+"Artwork Unavailable" = "Omslag inte tillgängligt";
+"This track has no artwork available." = "Det här spåret har inget omslag tillgängligt.";

Sources/Kaset/Resources/tr.lproj/Localizable.strings

@@ -566,3 +566,7 @@
 "Start a new chat to continue." = "Devam etmek için yeni bir sohbet başlatın.";
 "Ask Gemini response ready" = "Gemini'ye Sor yanıtı hazır";
 "New Ask Gemini chat ready" = "Yeni Gemini sohbeti hazır";
+"View Artwork" = "Kapak Görselini Görüntüle";
+"Album Artwork" = "Albüm Kapak Görseli";
+"Artwork Unavailable" = "Kapak Görseli Kullanılamıyor";
+"This track has no artwork available." = "Bu parça için kapak görseli yok.";

Sources/Kaset/Resources/uk.lproj/Localizable.strings

@@ -566,3 +566,7 @@
 "Start a new chat to continue." = "Почніть новий чат, щоб продовжити.";
 "Ask Gemini response ready" = "Відповідь «Запитати Gemini» готова";
 "New Ask Gemini chat ready" = "Новий чат «Запитати Gemini» готовий";
+"View Artwork" = "Переглянути обкладинку";
+"Album Artwork" = "Обкладинка альбому";
+"Artwork Unavailable" = "Обкладинка недоступна";
+"This track has no artwork available." = "Для цього треку немає обкладинки.";

Sources/Kaset/Resources/zh-Hans.lproj/Localizable.strings

@@ -564,3 +564,7 @@
 "e.g., Remove slow songs, reorder by energy..." = "例如：移除慢歌、按能量重新排序…";
 "songs" = "首歌曲";
 "tracks" = "首曲目";
+"View Artwork" = "查看封面";
+"Album Artwork" = "专辑封面";
+"Artwork Unavailable" = "无可用封面";
+"This track has no artwork available." = "此曲目没有可用封面。";

Sources/Kaset/Resources/zh-Hant.lproj/Localizable.strings

@@ -564,3 +564,7 @@
 "e.g., Remove slow songs, reorder by energy..." = "例如：移除慢歌、依能量重新排序…";
 "songs" = "首歌曲";
 "tracks" = "首曲目";
+"View Artwork" = "查看封面";
+"Album Artwork" = "專輯封面";
+"Artwork Unavailable" = "無可用封面";
+"This track has no artwork available." = "此曲目沒有可用封面。";

Sources/Kaset/Utilities/Extensions.swift

@@ -69,6 +69,39 @@ extension URL {
 
         return URL(string: urlString)
     }
+
+    /// Returns a square variant of a YouTube artwork URL at the requested pixel size.
+    ///
+    /// YouTube's image hosts encode the served dimensions in a `w<N>-h<N>` option suffix
+    /// (`…=w544-h544-l90-rj`). `highQualityThumbnailURL` only lifts list-sized thumbnails to
+    /// 226px, so full-size surfaces must request their own dimensions. Hosts serve at most
+    /// the source resolution, so an oversized request degrades to the original artwork.
+    func artworkURL(side: Int) -> URL? {
+        guard side > 0,
+              host?.contains("ytimg.com") == true || host?.contains("googleusercontent.com") == true
+        else { return self }
+
+        let absolute = absoluteString
+        guard let separatorIndex = absolute.lastIndex(of: "=") else { return self }
+
+        let base = absolute[absolute.startIndex ..< separatorIndex]
+        let options = absolute[absolute.index(after: separatorIndex)...]
+        guard !options.isEmpty else { return self }
+
+        var didResize = false
+        let rescaled = options.split(separator: "-").map { token -> String in
+            guard let prefix = token.first,
+                  prefix == "w" || prefix == "h",
+                  token.count > 1,
+                  token.dropFirst().allSatisfy(\.isNumber)
+            else { return String(token) }
+            didResize = true
+            return "\(prefix)\(side)"
+        }
+
+        guard didResize else { return self }
+        return URL(string: base + "=" + rescaled.joined(separator: "-")) ?? self
+    }
 }
 
 // MARK: - String Extensions

Sources/Kaset/Views/ArtworkViewer.swift

@@ -0,0 +1,147 @@
+import SwiftUI
+
+// MARK: - ArtworkViewerSource
+
+/// Resolves which artwork URL the viewer should display.
+///
+/// The API-provided artwork is preferred, falling back to YouTube's public video
+/// thumbnail when that source fails, mirroring `SongThumbnailView`.
+struct ArtworkViewerSource: Equatable {
+    let primaryURL: URL?
+    let fallbackURL: URL?
+
+    var hasArtwork: Bool {
+        self.primaryURL != nil || self.fallbackURL != nil
+    }
+
+    /// The distinct fallback, if the primary is worth retrying past.
+    var retryableFallbackURL: URL? {
+        guard let fallbackURL, fallbackURL != self.primaryURL else { return nil }
+        return fallbackURL
+    }
+
+    func activeURL(didFailPrimary: Bool) -> URL? {
+        if didFailPrimary, let retryableFallbackURL {
+            return retryableFallbackURL
+        }
+        return self.primaryURL ?? self.fallbackURL
+    }
+}
+
+// MARK: - ArtworkViewer
+
+/// A sheet that displays album artwork at high resolution.
+///
+/// Shows the image centered with a dark background. The viewer can be dismissed
+/// by tapping anywhere, pressing Escape, or clicking the close button in the top-right corner.
+struct ArtworkViewer: View {
+    /// Album artwork is square, so the viewer is square too. Scaled against the active
+    /// screen so it stays generous on large displays without overflowing small ones.
+    private static var viewerSide: CGFloat {
+        guard let visibleFrame = NSScreen.main?.visibleFrame else { return 560 }
+        let side = min(visibleFrame.width, visibleFrame.height) * 0.62
+        return min(700, max(380, side.rounded()))
+    }
+
+    /// Source artwork is requested well above the display size so the image stays crisp
+    /// on Retina displays; hosts cap the response at the original resolution.
+    private static let requestedArtworkPixels = 1200
+
+    /// The high-quality thumbnail URL to display.
+    let artworkURL: URL?
+
+    /// Public video thumbnail used when `artworkURL` fails to load.
+    var fallbackArtworkURL: URL?
+
+    /// Called when the viewer should be dismissed.
+    let onDismiss: () -> Void
+
+    @State private var didFailPrimary = false
+    @State private var didFailArtwork = false
+
+    private var source: ArtworkViewerSource {
+        ArtworkViewerSource(primaryURL: self.artworkURL, fallbackURL: self.fallbackArtworkURL)
+    }
+
+    /// The chosen source before any size upgrade; failure handling is keyed on this.
+    private var activeSourceURL: URL? {
+        self.source.activeURL(didFailPrimary: self.didFailPrimary)
+    }
+
+    private func displayURL(for sourceURL: URL) -> URL {
+        sourceURL.artworkURL(side: Self.requestedArtworkPixels) ?? sourceURL
+    }
+
+    var body: some View {
+        ZStack {
+            self.backgroundLayer
+
+            if let sourceURL = self.activeSourceURL, !self.didFailArtwork {
+                CachedAsyncImage(
+                    url: self.displayURL(for: sourceURL),
+                    targetSize: CGSize(width: Self.viewerSide, height: Self.viewerSide),
+                    onFailure: { self.handleFailure(of: sourceURL) },
+                    content: { image in
+                        image
+                            .resizable()
+                            .aspectRatio(contentMode: .fit)
+                    }
+                )
+                .id(sourceURL)
+                .frame(maxWidth: .infinity, maxHeight: .infinity)
+                .padding(24)
+                .accessibilityLabel(Text(String(localized: "Album Artwork")))
+            } else {
+                self.unavailableArtwork
+            }
+        }
+        .contentShape(Rectangle())
+        .onTapGesture {
+            self.onDismiss()
+        }
+        .overlay(alignment: .topTrailing) {
+            self.closeButton
+                .padding(20)
+        }
+        .frame(width: Self.viewerSide, height: Self.viewerSide)
+        .background(Color.black)
+    }
+
+    // MARK: - Actions
+
+    private func handleFailure(of url: URL) {
+        if url == self.source.primaryURL, self.source.retryableFallbackURL != nil {
+            self.didFailPrimary = true
+            return
+        }
+        self.didFailArtwork = true
+    }
+
+    // MARK: - Subviews
+
+    private var backgroundLayer: some View {
+        Color.black.opacity(0.85)
+    }
+
+    private var unavailableArtwork: some View {
+        ContentUnavailableView {
+            Label(String(localized: "Artwork Unavailable"), systemImage: "photo")
+        } description: {
+            Text(String(localized: "This track has no artwork available."))
+        }
+        .foregroundStyle(.white.opacity(0.7))
+        .frame(maxWidth: .infinity, maxHeight: .infinity)
+    }
+
+    private var closeButton: some View {
+        Button {
+            self.onDismiss()
+        } label: {
+            Image(systemName: "xmark.circle.fill")
+                .font(.system(size: 28))
+                .foregroundStyle(.white.opacity(0.8))
+        }
+        .buttonStyle(.plain)
+        .accessibilityLabel(Text(String(localized: "Close")))
+    }
+}