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/lib/mock/client.ts

@@ -156,11 +156,42 @@ export class MockGateway implements GatewayClient {
   }
 
   // --- lobby ---
-  async lobbyEnqueue(variant: Variant, multipleWords: boolean): Promise<MatchResult> {
+  async lobbyEnqueue(variant: Variant, multipleWords: boolean, vsAi: boolean): Promise<MatchResult> {
+    const id = crypto.randomUUID();
+    if (vsAi) {
+      // An honest-AI game starts active, already seated with a robot (rendered as 🤖 from the
+      // vs_ai flag); there is no open/wait phase.
+      const ai: MockGame = {
+        view: {
+          id,
+          variant,
+          dictVersion: 'v1',
+          status: 'active',
+          players: 2,
+          toMove: 0,
+          turnTimeoutSecs: 604800,
+          multipleWordsPerTurn: multipleWords,
+          moveCount: 0,
+          endReason: '',
+          lastActivityUnix: Math.floor(Date.now() / 1000),
+          vsAi: true,
+          seats: [
+            { seat: 0, accountId: ME, displayName: 'You', score: 0, hintsUsed: 0, isWinner: false },
+            { seat: 1, accountId: 'robot', displayName: 'Robot', score: 0, hintsUsed: 0, isWinner: false },
+          ],
+        },
+        moves: [],
+        rack: draw(variant, 7),
+        bagLen: 86,
+        hintsRemaining: 1,
+        chat: [],
+      };
+      this.games.set(id, ai);
+      return { matched: true, game: structuredClone(ai.view) };
+    }
     // The player enters an open game immediately and waits inside it; a robot opponent takes
     // the empty seat shortly (a sped-up version of the backend's 90–180 s wait), pushing
     // opponent_joined so the game UI restores from the "searching for opponent" state.
-    const id = crypto.randomUUID();
     const g: MockGame = {
       view: {
         id,
@@ -174,6 +205,7 @@ export class MockGateway implements GatewayClient {
         moveCount: 0,
         endReason: '',
         lastActivityUnix: Math.floor(Date.now() / 1000),
+        vsAi: false,
         seats: [
           { seat: 0, accountId: ME, displayName: 'You', score: 0, hintsUsed: 0, isWinner: false },
           { seat: 1, accountId: '', displayName: '', score: 0, hintsUsed: 0, isWinner: false },