feat(05-04): calendar API client, calendar widget, registry wiring

- calendar-api.ts: fetchSources/addSource/updateSource/deleteSource/testSource/fetchEvents with credentials:'include'
- calendar-widget.tsx: upcoming-events list with source color dots, three empty states (no sources/no events/loading)
- widget-registry.tsx: wireCalendarWidget() replaces placeholder with real CalendarWidget
- page.tsx: wires CalendarWidget into registry on mount
- i18n: added calendar.loading key to de.json and en.json

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

apps/web/src/app/(portal)/page.tsx

@@ -5,9 +5,10 @@ import { useTranslations } from 'next-intl';
 import { DashboardGrid } from '@/components/dashboard/dashboard-grid';
 import { EditModeToggle } from '@/components/dashboard/edit-mode-toggle';
 import { WidgetCatalogModal } from '@/components/dashboard/widget-catalog-modal';
-import { wireClockWidget, wireSearchWidget, wireNoteWidget } from '@/components/dashboard/widget-registry';
+import { wireClockWidget, wireSearchWidget, wireCalendarWidget, wireNoteWidget } from '@/components/dashboard/widget-registry';
 import { ClockWidget } from '@/components/dashboard/widgets/clock-widget';
 import { SearchWidget } from '@/components/dashboard/widgets/search-widget';
+import { CalendarWidget } from '@/components/dashboard/widgets/calendar-widget';
 import { NoteWidget } from '@/components/dashboard/widgets/note-widget';
 import { useDashboardStore } from '@/lib/stores/dashboard-store';
 import type { WidgetType } from '@/components/dashboard/widget-registry';
@@ -15,6 +16,7 @@ import type { WidgetType } from '@/components/dashboard/widget-registry';
 // Wire widget components into the registry (deferred to avoid circular deps)
 wireClockWidget(ClockWidget);
 wireSearchWidget(SearchWidget);
+wireCalendarWidget(CalendarWidget);
 wireNoteWidget(NoteWidget);
 
 export default function DashboardPage() {