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/online/signalr-service.ts

@@ -293,4 +293,6 @@ export class SignalrService implements OnlineService {
   buyItem(id: string) { return this.mock.buyItem(id); }
   getDailyState(): Promise<DailyRewardState> { return this.mock.getDailyState(); }
   claimDaily(): Promise<{ reward: number; profile: UserProfile; day: number }> { return this.mock.claimDaily(); }
+  getCoinPacks() { return this.mock.getCoinPacks(); }
+  buyCoins(id: string) { return this.mock.buyCoins(id); }
 }