feat(desktop): grid nativo e recorte magnetico de captura

[RenanMev]

Summary

• Adiciona captura nativa com xcap: grid de janelas/monitores com thumbnail, titulo real e exclusao das janelas do proprio Linvo
• Overlay fullscreen com tela congelada e magnetismo via UI Automation (ElementFromPoint), com recorte livre por arraste e fallback getDisplayMedia
• Liga o menu do composer em tres caminhos: escolher fonte, recorte magnetico e seletor do sistema

Test plan

• cargo check no src-tauri
• tsc --noEmit no desktop
• Vitest focado: 31 testes (menu, hook, close do overlay, helpers)
• Manual: abrir grid, capturar janela, confirmar no preview
• Manual: Recorte magnetico — hover destaca elemento, Enter confirma, Esc cancela
• Manual: fallback "Seletor do sistema" ainda funciona

Relacionado

• Preview/recorte TS (ja mergeado): feat(desktop): preview e recorte antes de anexar a captura #10
• API de anexos (ja mergeada): https://github.com/RenanMev/linvo-api/pull/14

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Note

Medium Risk
Screen-capture and overlay behavior are platform-sensitive (permissions, multi-monitor sizing, large base64 payloads), and magnetic snapping depends on Windows COM/UIA with non-Windows degradation; xcap adds a sizable native dependency surface.

Overview
Native visual context capture replaces the composer’s direct “capture window / full screen” actions with three paths: a thumbnail grid of windows and monitors (via xcap), magnetic crop on a frozen multi-monitor snapshot, and the existing getDisplayMedia system picker.

The Tauri side adds a capture module with commands to list sources (with thumbnails, titles, and Linvo self-window exclusion), capture PNG bytes/metadata, open/close a dedicated capture-overlay webview spanning the virtual desktop, and on Windows resolve element bounds under the cursor via UI Automation (ElementFromPoint) with HWND fallback. Capabilities and capture.toml permissions wire these invokes; Cargo.toml pulls in xcap, image, base64, and Windows accessibility crates.

The React layer adds CaptureSourcePicker, CaptureOverlayApp (drag selection, debounced magnet highlight, Enter/Esc), and extends useDisplaySnapshot with picker state, native source capture into the existing preview/crop draft flow, and overlay result/cancel listeners. ChatInput menu and tests are updated accordingly; window chrome treats capture-overlay close as hiding the overlay.

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