feat: dashboard manifest supports 'supported_games' field, frontend filters by selected game

- DashboardTheme model adds supported_games (default: 'all')
- Built-in dashboards declare game compatibility:
  speedometer/tachometer/gear_indicator -> all
  lap_timer -> forza_horizon_5,forza_horizon_4,forza_motorsport,f1_24
- Dashboard browser filters themes by selected game
- Card shows '全' (all) or '限' (limited) badge
- Updated DASHBOARD_DEV.md with supported_games spec

dashboards/lap_timer/manifest.json

@@ -2,9 +2,10 @@
     "id": "lap_timer",
     "name": "圈速计时器",
     "category": "timing",
-    "description": "当前圈速、最佳圈和上圈时间对比显示",
+    "description": "当前圈速、最佳圈和上圈时间对比显示。仅支持 Forza 系列和 F1",
     "author": "Yei.J. (AskaEth)",
     "version": "1.0.0",
+    "supported_games": "forza_horizon_5,forza_horizon_4,forza_motorsport,f1_24",
     "config": {
         "icon": "⏱️",
         "aspect_ratio": "4:3",