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/store/authStore.ts

@@ -66,6 +66,9 @@ interface AuthState {
   discordTemplateState: string;
   discordTemplateLargeText: string;
   useCustomTitlebar: boolean;
+  /** Pre-build the mini-player webview at app start on Linux/macOS so content is available instantly
+   *  on first open. Ignored on Windows — that platform always pre-creates as a hang workaround. */
+  preloadMiniPlayer: boolean;
   /** Linux WebKitGTK: smooth wheel on when true; off only after explicit opt-out in Settings. */
   linuxWebkitKineticScroll: boolean;
   nowPlayingEnabled: boolean;
@@ -212,6 +215,7 @@ interface AuthState {
   setDiscordTemplateState: (v: string) => void;
   setDiscordTemplateLargeText: (v: string) => void;
   setUseCustomTitlebar: (v: boolean) => void;
+  setPreloadMiniPlayer: (v: boolean) => void;
   setLinuxWebkitKineticScroll: (v: boolean) => void;
   setNowPlayingEnabled: (v: boolean) => void;
   setLyricsServerFirst: (v: boolean) => void;
@@ -318,6 +322,7 @@ export const useAuthStore = create<AuthState>()(
       discordTemplateState: '{album}',
       discordTemplateLargeText: '{album}',
       useCustomTitlebar: false,
+      preloadMiniPlayer: false,
       linuxWebkitKineticScroll: true,
       nowPlayingEnabled: false,
       lyricsServerFirst: true,
@@ -448,6 +453,7 @@ export const useAuthStore = create<AuthState>()(
       setDiscordTemplateState: (v) => set({ discordTemplateState: v }),
       setDiscordTemplateLargeText: (v) => set({ discordTemplateLargeText: v }),
       setUseCustomTitlebar: (v) => set({ useCustomTitlebar: v }),
+      setPreloadMiniPlayer: (v) => set({ preloadMiniPlayer: v }),
       setLinuxWebkitKineticScroll: (v) => set({ linuxWebkitKineticScroll: v }),
       setNowPlayingEnabled: (v) => set({ nowPlayingEnabled: v }),
       setLyricsServerFirst: (v: boolean) => set({ lyricsServerFirst: v }),