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").

backend/internal/adminconsole/templates/pages/games.gohtml

@@ -8,11 +8,11 @@
 <a href="/_gm/games?status=finished"{{if eq .Status "finished"}} class="active"{{end}}>finished</a>
 </nav>
 <table class="list">
-<thead><tr><th>Game</th><th>Variant</th><th>Status</th><th class="num">Players</th><th>Updated</th></tr></thead>
+<thead><tr><th>Game</th><th>Variant</th><th>Status</th><th>🤖</th><th class="num">Players</th><th>Updated</th></tr></thead>
 <tbody>
 {{range .Items}}
-<tr><td><a href="/_gm/games/{{.ID}}">{{.ID}}</a></td><td>{{.Variant}}</td><td>{{.Status}}</td><td class="num">{{.Players}}</td><td>{{.UpdatedAt}}</td></tr>
-{{else}}<tr><td colspan="5"><span class="note">no games</span></td></tr>{{end}}
+<tr><td><a href="/_gm/games/{{.ID}}">{{.ID}}</a></td><td>{{.Variant}}</td><td>{{.Status}}</td><td>{{if .VsAI}}🤖{{end}}</td><td class="num">{{.Players}}</td><td>{{.UpdatedAt}}</td></tr>
+{{else}}<tr><td colspan="6"><span class="note">no games</span></td></tr>{{end}}
 </tbody>
 </table>
 <nav class="pager">