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/transport.ts

@@ -84,8 +84,8 @@ export function createTransport(baseUrl: string): GatewayClient {
       return codec.decodeGameList(await exec('games.list', codec.empty()));
     },
 
-    async lobbyEnqueue(variant, multipleWords) {
-      return codec.decodeMatchResult(await exec('lobby.enqueue', codec.encodeEnqueue(variant, multipleWords)));
+    async lobbyEnqueue(variant, multipleWords, vsAi) {
+      return codec.decodeMatchResult(await exec('lobby.enqueue', codec.encodeEnqueue(variant, multipleWords, vsAi)));
     },
     async lobbyPoll() {
       return codec.decodeMatchResult(await exec('lobby.poll', codec.empty()));