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/screens/Lobby.svelte

@@ -63,6 +63,8 @@
   function opponents(g: GameView): string {
     // An auto-match game still waiting for an opponent shows the "searching" placeholder.
     if (g.status === 'open') return t('game.searchingForOpponent');
+    // An honest-AI game shows the robot opponent as 🤖, never its (pooled) name.
+    if (g.vsAi) return '🤖';
     return g.seats
       .filter((s) => s.accountId !== myId)
       .map((s) => s.displayName)

ui/src/screens/NewGame.svelte

@@ -39,6 +39,9 @@
 
   const guest = $derived(app.profile?.isGuest ?? true);
   let mode = $state<'auto' | 'friends'>('auto');
+  // The quick-game opponent: an honest AI (a robot that joins and moves at once, shown as 🤖)
+  // or a random human via auto-match. AI is the default.
+  let opponent = $state<'ai' | 'random'>('ai');
 
   // --- auto-match ---
   // Enqueue drops the player straight into a real game — a freshly opened one awaiting an
@@ -51,7 +54,7 @@
     if (starting) return;
     starting = true;
     try {
-      const r = await gateway.lobbyEnqueue(v, multipleWordsForRequest(v, multipleWords));
+      const r = await gateway.lobbyEnqueue(v, multipleWordsForRequest(v, multipleWords), opponent === 'ai');
       if (r.game) navigate(`/game/${r.game.id}`);
     } catch (e) {
       handleError(e);
@@ -119,7 +122,10 @@
       {/if}
 
       {#if mode === 'auto'}
-        <p class="subtitle">{t('new.subtitle')}</p>
+        <div class="seg modes">
+          <button class="opt" class:active={opponent === 'ai'} onclick={() => (opponent = 'ai')}>🤖 {t('new.opponentAI')}</button>
+          <button class="opt" class:active={opponent === 'random'} onclick={() => (opponent = 'random')}>👤 {t('new.opponentRandom')}</button>
+        </div>
         <div class="variants">
           {#each variants as v (v.id)}
             <button
@@ -146,8 +152,8 @@
             <input type="checkbox" bind:checked={multipleWords} />
           </label>
         {/if}
-        <p class="movelimit">{t('new.moveLimit', { n: AUTO_MATCH_HOURS })}</p>
-        <p class="searchhint">{t('new.searchHint')}</p>
+        <p class="movelimit">{opponent === 'ai' ? t('new.aiInactiveLimit') : t('new.moveLimit', { n: AUTO_MATCH_HOURS })}</p>
+        {#if opponent === 'random'}<p class="searchhint">{t('new.searchHint')}</p>{/if}
         <button
           class="invite"
           disabled={!selectedAuto || !connection.online || starting}