Split card design into front+back, add sound effects & background music

Card design:
- Separate cardFront + cardBack (each own/equip independently)
- Fronts: classic (free), ivory/rosegold (buy), parchment/mint (earned)
- Backs: classic (free), sapphire/emerald (buy), ruby/royal (earned)
- PlayingCard `front` prop; table applies front to all faces, back to opponents
- Profile has front + back pickers; shop has both sections

Audio:
- Web Audio synth engine (no asset files): SFX for card/deal/trump/trick,
  win/lose, message, notify, award, levelup, purchase, kot + ambient music
- Toggles in profile (Audio) + mute button in game HUD; prefs persisted
- Wired across game-store, rewards, daily, shop, chat

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

src/lib/session-store.ts

@@ -22,7 +22,7 @@ interface SessionStore {
   signOut: () => Promise<void>;
 
   updateProfile: (
-    patch: Partial<Pick<UserProfile, "displayName" | "avatar" | "avatarImage" | "title" | "cardStyle">>
+    patch: Partial<Pick<UserProfile, "displayName" | "avatar" | "avatarImage" | "title" | "cardFront" | "cardBack">>
   ) => Promise<void>;
   upgradePlan: () => Promise<void>;
 }