feat: AI-game refinements (GCG, your_turn, admin, metrics)

Follow-ups on the honest-AI game, same PR:
- GCG export labels the robot seat "AI" instead of its pool name (ExportGCG
  overrides via accounts.IsRobot); the in-app 🤖 is unchanged.
- vs_ai games emit no your_turn (the robot replies instantly, so it would be
  redundant); opponent_moved still advances the UI.
- Admin console shows the AI flag: a 🤖 column in /games and an "AI game" line
  on the game card (GameRow/GameDetailView gain VsAI).
- games_started_total / games_abandoned_total gain a vs_ai attribute; the
  Grafana Game-domain dashboard splits started/abandoned into human and AI
  panels.

Tests: metrics unit (vs_ai split); integration (no your_turn, GCG "AI").

docs/ARCHITECTURE.md

@@ -378,7 +378,11 @@ the robot package), with the periodic driver as the fallback. There is **no shor
 timeout**; instead the game is created with `turn_timeout_secs = AIInactivityTimeout` (**7
 days**) and the existing turn-timeout sweeper resigns the overdue seat — since the robot moves
 at once, only the human is ever on the clock, so the per-turn timeout doubles as the
-"abandoned after 7 days of inactivity → loss" rule with no new column or sweeper.
+"abandoned after 7 days of inactivity → loss" rule with no new column or sweeper. An AI
+game emits **no `your_turn`** (the instant reply makes it redundant; `opponent_moved`
+still advances the UI), its **GCG export labels the robot seat "AI"**, and the
+games-started / -abandoned metrics carry a **`vs_ai`** attribute so AI and human games
+chart separately (the admin `/games` list and game card also show the AI flag).
 
 The robot keeps **no per-game state**: every choice is derived deterministically
 from the game's bag `seed` (a restart-stable FNV-1a mix), so a background driver