Fix: in-game mute button now mutes background music too

HUD mute is a master toggle (sound effects + music) via sound-store.toggleAll;
icon reflects fully-muted state.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

src/lib/sound-store.ts

@@ -8,6 +8,8 @@ interface SoundStore {
   music: boolean;
   toggleSfx: () => void;
   toggleMusic: () => void;
+  /** Master mute: turns BOTH sfx and music off (or both back on). */
+  toggleAll: () => void;
 }
 
 export const useSoundStore = create<SoundStore>((set, get) => ({
@@ -23,4 +25,11 @@ export const useSoundStore = create<SoundStore>((set, get) => ({
     sound.setMusicEnabled(v);
     set({ music: v });
   },
+  toggleAll: () => {
+    // If anything is on, mute everything; otherwise turn everything back on.
+    const v = !(get().sfx || get().music);
+    sound.setSfxEnabled(v);
+    sound.setMusicEnabled(v);
+    set({ sfx: v, music: v });
+  },
 }));