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/server/handlers_admin_console.go

@@ -406,7 +406,7 @@ func (s *Server) consoleGameDetail(c *gin.Context) {
 		ID: g.ID.String(), Variant: g.Variant.String(), DictVersion: g.DictVersion,
 		Status: g.Status, Players: g.Players, ToMove: g.ToMove, EndReason: g.EndReason,
 		MoveCount: g.MoveCount, CreatedAt: fmtTime(g.CreatedAt), UpdatedAt: fmtTime(g.UpdatedAt),
-		FinishedAt: fmtTimePtr(g.FinishedAt),
+		FinishedAt: fmtTimePtr(g.FinishedAt), VsAI: g.VsAI,
 	}
 	// Resolve seats and detect robot seats; capture the human opponent's timezone, which
 	// anchors the robot's sleep window for the next-move ETA.
@@ -1021,7 +1021,7 @@ func (s *Server) consoleUUID(c *gin.Context, back string) (uuid.UUID, bool) {
 
 // gameRow projects a game summary into its console row.
 func gameRow(g game.Game) adminconsole.GameRow {
-	return adminconsole.GameRow{ID: g.ID.String(), Variant: g.Variant.String(), Status: g.Status, Players: g.Players, UpdatedAt: fmtTime(g.UpdatedAt)}
+	return adminconsole.GameRow{ID: g.ID.String(), Variant: g.Variant.String(), Status: g.Status, Players: g.Players, UpdatedAt: fmtTime(g.UpdatedAt), VsAI: g.VsAI}
 }
 
 // trimForm returns the trimmed value of a posted form field.