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-tauri/src/lib.rs

@@ -2764,6 +2764,19 @@ fn build_mini_player_window(
         .map_err(|e| format!("failed to build mini player window: {e}"))
 }
 
+/// Pre-build the mini player window hidden, so the first `open_mini_player`
+/// call becomes a pure show/hide and the user sees content instantly. On
+/// Windows this already happens unconditionally in `.setup()` as a hang
+/// workaround; this command is used by Linux/macOS when the user opts into
+/// the `preloadMiniPlayer` setting. Idempotent — no-op if the window exists.
+#[tauri::command]
+fn preload_mini_player(app: tauri::AppHandle) -> Result<(), String> {
+    if app.get_webview_window("mini").is_some() {
+        return Ok(());
+    }
+    build_mini_player_window(&app, false).map(|_| ())
+}
+
 /// Open (or toggle) the mini player window. On platforms where the window
 /// was pre-created at startup (Windows), this is a pure show/hide. On
 /// other platforms the window is created lazily on first call.
@@ -3132,6 +3145,7 @@ pub fn run() {
             no_compositing_mode,
             is_tiling_wm_cmd,
             open_mini_player,
+            preload_mini_player,
             close_mini_player,
             set_mini_player_always_on_top,
             resize_mini_player,