feat: remote AI dispatch + Settings + secure storage + release pipeline

[aymandakirgh]

Everything fixable in code toward production. Stacks on the MVP PR (#3) — review/merge that first.

The differentiator: remote AI dispatch

The command bar now actually does what the README promises. Unrecognized queries (anything the local handlers don't resolve) dispatch to a user-configured AI backend.

• AIDispatching + OpenAICompatibleDispatcher — POSTs to any OpenAI-compatible /chat/completions (OpenAI, Ollama local, proxies). Injectable URLSession; typed errors.
• Privacy preserved — local-first is unchanged; nothing leaves the device unless you configure an endpoint and the query isn't handled locally. The 🔒/☁️ badge shows which path ran.
• Async submit() with a loading spinner.

Settings (⌘,)

• SettingsView — base URL, model, API key, OpenAI/Ollama presets, Save.
• SettingsStore — endpoint config → UserDefaults; API key → Keychain (KeychainSecretStore). SecretStoring protocol keeps the Keychain out of CI (tests use InMemorySecretStore).
• App now exposes a real Settings scene (was EmptyView).

UX fix

The panel no longer collapses out from under you while typing — hover-leave only collapses when the command bar is idle (shouldStayOpen).

Production infra

• .github/workflows/release.yml — on a v* tag: build → (sign + notarize if secrets present) → DMG → GitHub Release. Gated: produces an unsigned DMG today, a signed+notarized one once the Apple cert secrets exist.
• RELEASING.md — exact secrets + steps, and the standing blocker spelled out.

Tests (+15 assertions)

AIDispatcherTests (stub URLProtocol: success/HTTP-error/empty/unconfigured), AISettingsTests (URL building, config, persistence round-trip), CommandBarViewModelTests (local resolve, remote dispatch, unconfigured hint, stay-open). CI runs them on this PR.

Still NOT production — unchanged blockers

1. Never been run. All of this is CI-verified (compiles + unit tests), but the UI — Settings window, command-bar focus, spinner, the collapse fix — has not been seen by a human. Needs Xcode on a notched Mac.
2. Can't be distributed until GH enrolls in the Apple Developer Program ($99/yr) and the signing secrets are added. The pipeline is ready and waiting for exactly that.

Not in scope: media controls, calendar, file shelf, system HUD; streaming AI responses; conversation history.

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