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").

deploy/grafana/dashboards/game-domain.json

@@ -4,24 +4,34 @@
   "tags": ["scrabble"],
   "timezone": "",
   "schemaVersion": 39,
-  "version": 2,
+  "version": 3,
   "refresh": "30s",
   "time": { "from": "now-24h", "to": "now" },
   "panels": [
     {
       "type": "timeseries",
-      "title": "Games started / abandoned (rate by variant)",
+      "title": "Games started / abandoned — human (rate by variant)",
       "gridPos": { "h": 8, "w": 12, "x": 0, "y": 0 },
       "datasource": { "type": "prometheus", "uid": "prometheus" },
       "targets": [
-        { "refId": "A", "expr": "sum(rate(games_started_total[15m])) by (variant)", "legendFormat": "started {{variant}}" },
-        { "refId": "B", "expr": "sum(rate(games_abandoned_total[15m])) by (variant)", "legendFormat": "abandoned {{variant}}" }
+        { "refId": "A", "expr": "sum(rate(games_started_total{vs_ai=\"false\"}[15m])) by (variant)", "legendFormat": "started {{variant}}" },
+        { "refId": "B", "expr": "sum(rate(games_abandoned_total{vs_ai=\"false\"}[15m])) by (variant)", "legendFormat": "abandoned {{variant}}" }
+      ]
+    },
+    {
+      "type": "timeseries",
+      "title": "Games started / abandoned — AI (rate by variant)",
+      "gridPos": { "h": 8, "w": 12, "x": 12, "y": 0 },
+      "datasource": { "type": "prometheus", "uid": "prometheus" },
+      "targets": [
+        { "refId": "A", "expr": "sum(rate(games_started_total{vs_ai=\"true\"}[15m])) by (variant)", "legendFormat": "started {{variant}}" },
+        { "refId": "B", "expr": "sum(rate(games_abandoned_total{vs_ai=\"true\"}[15m])) by (variant)", "legendFormat": "abandoned {{variant}}" }
       ]
     },
     {
       "type": "timeseries",
       "title": "Robot games finished (rate)",
-      "gridPos": { "h": 8, "w": 12, "x": 12, "y": 0 },
+      "gridPos": { "h": 8, "w": 12, "x": 12, "y": 24 },
       "datasource": { "type": "prometheus", "uid": "prometheus" },
       "targets": [{ "refId": "A", "expr": "sum(rate(robot_games_finished_total[15m]))", "legendFormat": "robot games" }]
     },