feat(sasch40): improve Act III, add state persistence and fix portraits

- Fix character portrait crops and version assets to portrait_v2, ensuring correct identities (resolving Nat/Verena mismatch)
- Update Schankraum scene image and configure Nginx cache-control to prevent stale asset caching
- Make secret beer tap completely invisible in tavern until clicked
- Reposition room hotspots in Act III to eliminate overlapping click targets
- Add exit button [✕] to Bavarian Gstanzl duel minigame
- Implement localStorage persistence in gameStore to maintain progress across page reloads
- Enable clean game state and storage reset when clicking "Nochmal spielen"
- Expand automated playtest script to cover Nat dialogue, duel exit, reload persistence, and game restart

projects/sasch40/frontend/src/audio/synthAudio.ts

@@ -31,6 +31,13 @@ class SoundEngine {
     return this.isMuted
   }
 
+  public setMuted(val: boolean) {
+    this.isMuted = val
+    if (this.isMuted) {
+      this.stopBGM()
+    }
+  }
+
   // SFX: Kronkorken Collect (bright double ding)
   public playCoin() {
     if (this.isMuted) return