feat(08-01): registry foundation for 4 new widget types + Calculator widget (GREEN)

- widget-registry.tsx: extend WidgetType union with calculator/favorites/link/stopwatch
- widget-registry.tsx: add WIDGET_CONSTRAINTS entries with per-widget grid constraints (DASH-11)
- widget-registry.tsx: add SVG icons (CalculatorIcon, FavoritesIcon, LinkIcon, StopwatchIcon)
- widget-registry.tsx: add WIDGET_REGISTRY entries and wire functions for all 4 new types
- calculator-widget.tsx: full arithmetic implementation ported from personal-dashboard
  (parseDisplay, formatNumber, calculate, keyboard handler with stopPropagation)
- widget-catalog-modal.tsx: extend WIDGET_TYPES to include all 8 types
- create-widget.dto.ts: extend @IsIn to accept 8 widget types (T-08-01 mitigated)
- page.tsx: import CalculatorWidget and call wireCalculatorWidget()
- de.json / en.json: add i18n keys for calculator, favorites, link, stopwatch
- All 16 tests passing (GREEN)

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

@@ -5,11 +5,12 @@ 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, wireCalendarWidget, wireNoteWidget } from '@/components/dashboard/widget-registry';
+import { wireClockWidget, wireSearchWidget, wireCalendarWidget, wireNoteWidget, wireCalculatorWidget } 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 { CalculatorWidget } from '@/components/dashboard/widgets/calculator-widget';
 import { useDashboardStore } from '@/lib/stores/dashboard-store';
 import type { WidgetType } from '@/components/dashboard/widget-registry';
 
@@ -18,6 +19,7 @@ wireClockWidget(ClockWidget);
 wireSearchWidget(SearchWidget);
 wireCalendarWidget(CalendarWidget);
 wireNoteWidget(NoteWidget);
+wireCalculatorWidget(CalculatorWidget);
 
 export default function DashboardPage() {
   const t = useTranslations('widgets');