feat(mini-player): optional preload toggle for Linux + macOS

Adds a "Preload mini player" toggle in Settings → General → App behaviour
(off by default). When enabled, the mini webview is built hidden at app
start so the first open is instant, matching the Windows experience.
Costs one extra WebKit process running in the background (~50–100 MB).

Windows already pre-creates the mini unconditionally as a hang workaround
(commit 71fbc717); the toggle is hidden there and the invoke is skipped,
so that platform is untouched.

- authStore: new `preloadMiniPlayer: boolean` (default false) + setter.
- lib.rs: new `preload_mini_player` command; idempotent, no-op when the
  window already exists. Registered in the invoke handler.
- App.tsx: main window invokes `preload_mini_player` when the toggle is
  on and the platform is not Windows.
- Settings.tsx: toggle row under "Minimize to Tray", gated with
  `!IS_WINDOWS` so Windows users don't see it.
- i18n: `preloadMiniPlayer` + `preloadMiniPlayerDesc` added to all 8
  locales (en, de, es, fr, nb, nl, ru, zh).

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

src/App.tsx

@@ -56,7 +56,7 @@ import GenreDetail from './pages/GenreDetail';
 import ExportPickerModal from './components/ExportPickerModal';
 import AppUpdater from './components/AppUpdater';
 import TitleBar from './components/TitleBar';
-import { IS_LINUX } from './utils/platform';
+import { IS_LINUX, IS_WINDOWS } from './utils/platform';
 import { version } from '../package.json';
 import { useConnectionStatus } from './hooks/useConnectionStatus';
 import { useAuthStore } from './store/authStore';
@@ -975,6 +975,15 @@ export default function App() {
     return initMiniPlayerBridgeOnMain();
   }, [isMiniWindow]);
 
+  // Main window only: optionally pre-create the mini player webview hidden so
+  // the first open is instant. Windows already does this unconditionally in
+  // Rust .setup() as a hang workaround — skip here to avoid double-building.
+  const preloadMiniPlayer = useAuthStore(s => s.preloadMiniPlayer);
+  useEffect(() => {
+    if (isMiniWindow || IS_WINDOWS || !preloadMiniPlayer) return;
+    invoke('preload_mini_player').catch(() => {});
+  }, [isMiniWindow, preloadMiniPlayer]);
+
   // Mini window only: re-hydrate persisted appearance stores when the main
   // window writes new values. Both webviews share localStorage (same origin),
   // so the `storage` event fires here whenever main mutates a key — but