refactor(app): Phase D — move TauriEventBridge into src/app/ (#561)

Final piece of the App.tsx slim-down. The `TauriEventBridge` component
— ZIP download progress, track-preview lifecycle, audio device
changed/reset, the full `cli:*` listener surface (audio-device-set,
instant-mix, library list/set, server list/set, search, player-command),
tray-icon visibility sync, in-app keybindings keydown handler, media
keys + tray actions, `shortcut:global-action` / `shortcut:run-action`,
seek-relative / seek-absolute / set-volume, the window:close-requested
+ app:force-quit flow (with the shared `performExit` Orbit teardown),
and the `psysonic --info` snapshot publisher — moves into
`src/app/TauriEventBridge.tsx`.

`MainApp` imports it from the new file. `App.tsx` is now 57 LOC: just
the `App()` default-export that branches between `MiniPlayerApp` and
`MainApp` after wiring the shared theme / font / track-preview
document attributes.

A.K.A. App.tsx 1453 → 57 LOC over Phase 2 (M0 + B.1 + B.2 + C.1 + C.2
+ D). Pure code move at every step — no behaviour change.

Pre-PR check: PASS (frontend tests, tsc, coverage gates, prod build,
backend tests, clippy, backend coverage gates).

src/app/MainApp.tsx

@@ -14,7 +14,7 @@ import { initAudioListeners } from '../store/playerStore';
 import { initHotCachePrefetch } from '../hotCachePrefetch';
 import { initMiniPlayerBridgeOnMain } from '../utils/miniPlayerBridge';
 import { IS_WINDOWS } from '../utils/platform';
-import { TauriEventBridge } from '../App';
+import TauriEventBridge from './TauriEventBridge';
 import AppShell from './AppShell';
 import RequireAuth from './RequireAuth';