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.

backend/README.md

@@ -59,6 +59,16 @@ elapsed, and the waiting starter is told an opponent took the seat by an in-app
 **opponent_joined** push (carrying their refreshed game state) that fills the opponent card and
 re-enables resign and chat in place.
 
+The same robot also backs an **honest-AI quick game** (`games.vs_ai`), the alternative to the random
+path that the player chooses on New Game. `Matchmaker.StartVsAI` picks a pooled robot and creates a
+game **already seated and active** (random seat order) — it never enters the open pool. The robot
+driver has a `vs_ai` branch (no sleep, no proactive nudge, zero delay) plus a focused
+`DriveGame`/`TriggerMove` fast path wired from the game service's after-create/after-commit hook
+(`SetAITrigger`), so the robot replies the instant the player moves. AI games keep the same strength
+(`playToWin`), have **no per-move timeout** (`turn_timeout_secs = AIInactivityTimeout`, 7 days, so an
+abandoned game is lost after a week of inactivity — only the human is ever on the clock), record **no
+statistics** (skipped in `commit`), and disable chat/nudge (`social` `VsAI` → `ErrGameVsAI`).
+
 The backend opens to the edge. The route groups gain their first
 handlers (`internal/server/handlers_*.go`): gateway-only session endpoints under
 `/api/v1/internal` (Telegram/guest/email login → mint, resolve, revoke) and a