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/src/components/dashboard/dashboard-grid.test.tsx

@@ -1,6 +1,10 @@
 import { cleanup, render, screen } from '@testing-library/react';
 import { afterEach, describe, expect, it, vi } from 'vitest';
 
+// Mock CSS imports that vitest cannot resolve
+vi.mock('react-grid-layout/css/styles.css', () => ({}));
+vi.mock('react-resizable/css/styles.css', () => ({}));
+
 // Mock next-intl
 vi.mock('next-intl', () => ({
   useTranslations: (ns: string) => (key: string) => {