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/codec.test.ts

@@ -20,6 +20,7 @@ import {
   encodeCheckWord,
   encodeFeedbackSubmit,
   encodeDraftSave,
+  encodeEnqueue,
   encodeExchange,
   encodeStateRequest,
   encodeSubmitPlay,
@@ -27,6 +28,17 @@ import {
 } from './codec';
 
 describe('codec', () => {
+  it('encodes an enqueue request carrying the variant, word rule and vs_ai flag', () => {
+    for (const vsAi of [false, true]) {
+      const req = fb.EnqueueRequest.getRootAsEnqueueRequest(
+        new ByteBuffer(encodeEnqueue('scrabble_ru', false, vsAi)),
+      );
+      expect(req.variant()).toBe('scrabble_ru');
+      expect(req.multipleWordsPerTurn()).toBe(false);
+      expect(req.vsAi()).toBe(vsAi);
+    }
+  });
+
   it('round-trips a draft save request and view', () => {
     const json = '{"rack_order":"1,0","board_tiles":[]}';
     const req = fb.DraftRequest.getRootAsDraftRequest(new ByteBuffer(encodeDraftSave('g1', json)));
@@ -205,6 +217,7 @@ describe('codec', () => {
     fb.GameView.addEndReason(b, er);
     fb.GameView.addSeats(b, seats);
     fb.GameView.addLastActivityUnix(b, BigInt(1717000000));
+    fb.GameView.addVsAi(b, true);
     const game = fb.GameView.endGameView(b);
     const games = fb.GameList.createGamesVector(b, [game]);
     fb.GameList.startGameList(b);
@@ -217,6 +230,7 @@ describe('codec', () => {
     expect(gl.games[0].seats[0].displayName).toBe('Ann');
     expect(gl.games[0].seats[0].score).toBe(13);
     expect(gl.games[0].lastActivityUnix).toBe(1717000000);
+    expect(gl.games[0].vsAi).toBe(true);
   });
 
   it('decodes an OutgoingRequestList of account refs', () => {