feat: #2 G-force circle dashboard + .tsr export/import

- g_force dashboard: acceleration vector on 2G ring, lat/long G readout
- .tsr files export/import via API and UI
- Composite dashboard reverted (G-force is standalone)

dashboards/g_force/manifest.json

@@ -0,0 +1,14 @@
+{
+    "id": "g_force",
+    "name": "G 力圆图",
+    "category": "physics",
+    "description": "加速度向量实时可视化，圆心偏移表示纵向/横向G力方向和大小",
+    "author": "Yei.J. (AskaEth)",
+    "version": "1.0.0",
+    "supported_games": "all",
+    "config": {
+        "icon": "🎯",
+        "aspect_ratio": "1:1",
+        "render_mode": "contain"
+    }
+}