feat(05-01): dashboard grid, clock widget, widget registry, store, and tests

- Install react-grid-layout@2.2.3 and react-resizable
- Create widget-registry.tsx with all 4 widget types, WIDGET_CONSTRAINTS, WidgetProps
- Create dashboard-api.ts with fetch/save layout and widget CRUD functions
- Create dashboard-store.ts (Zustand, NO persist — D-05) with edit mode and auto-save on exit
- Create DashboardGrid with react-grid-layout v2 Responsive, ResizeObserver width
- Create ClockWidget using Intl.DateTimeFormat (no manual UTC offsets)
- Create WidgetWrapper with drag handle and delete button in edit mode
- Create EditModeToggle (pencil/checkmark), WidgetCatalogModal (2x2 grid)
- Rewrite portal page.tsx as dashboard with grid, edit toggle, widget catalog
- Add ResizeObserver polyfill in test setup, CSS mock support in vitest config
- All 5 tests green (dashboard grid + clock widget)

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

apps/web/package.json

@@ -16,6 +16,8 @@
     "next-themes": "^0.4.6",
     "react": "^19.0.0",
     "react-dom": "^19.0.0",
+    "react-grid-layout": "2.2.3",
+    "react-resizable": "^4.0.2",
     "zod": "^4.4.3",
     "zustand": "^5.0.14"
   },
@@ -26,6 +28,7 @@
     "@testing-library/user-event": "^14.6.1",
     "@types/react": "^19.0.0",
     "@types/react-dom": "^19.0.0",
+    "@types/react-grid-layout": "^2.1.0",
     "@vitejs/plugin-react": "^6.0.2",
     "jsdom": "^29.1.1",
     "postcss": "^8.0.0",