feat: honest AI opponent in quick game

New Game's quick game gains an explicit opponent selector — 🤖 AI (default)
or 👤 Random player. AI starts a game seated with a pooled robot that joins
and moves at once: no per-move timeout (a 7-day inactivity loss reusing the
turn-timeout sweeper), chat/nudge disabled, no statistics, the opponent shown
as 🤖 everywhere. The random path (disguised robot) is unchanged.

Driven by one game flag (games.vs_ai), set only on AI-started games so the
disguised path is never revealed; Matchmaker.StartVsAI seats the robot
directly (no open pool); the robot replies event-driven via the game service's
after-commit/after-create hook. Wire: vs_ai on EnqueueRequest + GameView.

ui/src/game/Game.svelte

@@ -869,6 +869,8 @@
   function seatName(s: { accountId: string; displayName: string } | undefined): string {
     if (!s) return '';
     if (s.accountId === app.session?.userId) return t('common.you');
+    // An honest-AI game shows the robot opponent as 🤖, never its (pooled human-like) name.
+    if (view?.game.vsAi) return '🤖';
     if (!s.accountId) return t('game.searchingForOpponent');
     return s.displayName;
   }
@@ -876,6 +878,7 @@
   // turnLabel is the under-board status when it is not the viewer's turn: the opponent's name
   // once they have joined, or a generic "opponent's turn" while the seat is still empty (waiting).
   function turnLabel(): string {
+    if (view?.game.vsAi) return '🤖';
     const s = view?.game.seats[view?.game.toMove ?? -1];
     if (s && s.accountId && s.accountId !== app.session?.userId) return s.displayName;
     return t('game.opponentsTurn');
@@ -885,6 +888,8 @@
   // (not the still-empty seat of an open game) who is not yet a friend (an already-requested
   // opponent still shows it, but disabled).
   function canAddFriend(accountId: string): boolean {
+    // Never offer add-friend against an AI opponent.
+    if (view?.game.vsAi) return false;
     return !!accountId && !app.profile?.isGuest && accountId !== app.session?.userId && !friends.has(accountId);
   }
 </script>