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/test/setup.ts

@@ -1 +1,20 @@
 import '@testing-library/jest-dom/vitest';
+
+// Polyfill ResizeObserver for jsdom (needed by react-grid-layout)
+if (typeof globalThis.ResizeObserver === 'undefined') {
+  globalThis.ResizeObserver = class ResizeObserver {
+    private callback: ResizeObserverCallback;
+    constructor(callback: ResizeObserverCallback) {
+      this.callback = callback;
+    }
+    observe() {
+      // Fire callback immediately with a mock entry
+      this.callback(
+        [{ contentRect: { width: 1200, height: 800 } } as unknown as ResizeObserverEntry],
+        this,
+      );
+    }
+    unobserve() {}
+    disconnect() {}
+  };
+}