Economy: free vs paid games + buy-coins page; friends remove confirmation

- Coins only matter for ranked: free games (vs computer / private friend rooms)
  cost nothing; random ranked requires an entry (stake), gated by balance →
  routes to buy-coins when short
- Buy Coins page (CoinPack/getCoinPacks/buyCoins; mock credits now, real
  Zarinpal/IDPay TODO); TopBar coins → buy; lobby create-room is Free
- Friends: removed instant red ✕ delete; UserMinus → inline confirm before remove

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

src/lib/ui-store.ts

@@ -12,18 +12,19 @@ export type Screen =
   | "matchmaking"
   | "leaderboard"
   | "shop"
+  | "buycoins"
   | "chat"
   | "notifications"
   | "game"; // the table (used for both ai + online)
 
 const ALL_SCREENS: Screen[] = [
   "home", "auth", "profile", "friends", "online",
-  "room", "matchmaking", "leaderboard", "shop", "chat", "notifications", "game",
+  "room", "matchmaking", "leaderboard", "shop", "buycoins", "chat", "notifications", "game",
 ];
 
 /** Screens safe to restore from a URL on a cold load (no transient state needed). */
 export const STATIC_SCREENS: Screen[] = [
-  "home", "auth", "profile", "friends", "online", "leaderboard", "shop", "notifications",
+  "home", "auth", "profile", "friends", "online", "leaderboard", "shop", "buycoins", "notifications",
 ];
 
 export function screenFromHash(): Screen {