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/components/dashboard/widget-catalog-modal.tsx

@@ -10,7 +10,16 @@ interface WidgetCatalogModalProps {
   onAddWidget: (type: WidgetType) => void;
 }
 
-const WIDGET_TYPES: WidgetType[] = ['clock', 'search', 'calendar', 'note'];
+const WIDGET_TYPES: WidgetType[] = [
+  'clock',
+  'search',
+  'calendar',
+  'note',
+  'calculator',
+  'favorites',
+  'link',
+  'stopwatch',
+];
 
 /**
  * Modal dialog showing available widget types as selectable cards.