HRV balanced dots, dashed gap lines, dashboard widgets + drag-to-edit layout

- Green dots for balanced HRV (joining orange unbalanced / red low) on the trend
- Trend charts bridge data gaps with a dashed line instead of a blank break
- Dashboard: drop Health today; add VO2 max, small sleep, and HRV status widgets
- Dashboard: editable widget grid (react-grid-layout) with drag/resize, saved per-user

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

frontend/package.json

@@ -9,24 +9,25 @@
     "preview": "vite preview"
   },
   "dependencies": {
-    "react": "^18.3.1",
-    "react-dom": "^18.3.1",
-    "react-router-dom": "^6.23.1",
-    "leaflet": "^1.9.4",
-    "react-leaflet": "^4.2.1",
-    "recharts": "^2.12.7",
-    "date-fns": "^3.6.0",
-    "clsx": "^2.1.1",
-    "zustand": "^4.5.2",
     "@tanstack/react-query": "^5.40.0",
     "axios": "^1.7.2",
-    "react-dropzone": "^14.2.3"
+    "clsx": "^2.1.1",
+    "date-fns": "^3.6.0",
+    "leaflet": "^1.9.4",
+    "react": "^18.3.1",
+    "react-dom": "^18.3.1",
+    "react-dropzone": "^14.2.3",
+    "react-grid-layout": "^1.5.3",
+    "react-leaflet": "^4.2.1",
+    "react-router-dom": "^6.23.1",
+    "recharts": "^2.12.7",
+    "zustand": "^4.5.2"
   },
   "devDependencies": {
     "@vitejs/plugin-react": "^4.3.1",
-    "vite": "^5.2.13",
     "autoprefixer": "^10.4.19",
     "postcss": "^8.4.38",
-    "tailwindcss": "^3.4.4"
+    "tailwindcss": "^3.4.4",
+    "vite": "^5.2.13"
   }
-}
+}