feat(mm): wait longer for a real opponent; add "start with bots now"

- server: a lone player in the online-league queue now keeps waiting (re-checking
  every 15s) up to 75s so an online opponent has a real chance to join; the moment
  a 2nd human queues they're matched together, and a full 4 still forms instantly.
  Add PlayNow hub method to force-start with bots on demand.
- client: matchmaking screen shows a "شروع با ربات / Start with bots" button after
  a few seconds so the player can skip the wait; waiting copy updated; raise the
  "connection stuck" hint threshold to 90s so it no longer fires during normal waits.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

src/lib/online/signalr-service.ts

@@ -310,6 +310,10 @@ export class SignalrService implements OnlineService {
     this.emitMM("idle");
   }
 
+  async playNow() {
+    await this.conn?.invoke("PlayNow");
+  }
+
   onMatchmaking(cb: (s: MatchmakingState) => void): Unsubscribe {
     this.mmCbs.add(cb);
     return () => this.mmCbs.delete(cb);