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/messages/de.json

@@ -192,6 +192,38 @@
       "description": "Freitext-Notizen mit Markdown",
       "defaultTitle": "Notiz",
       "autosaveError": "Speichern fehlgeschlagen"
+    },
+    "calculator": {
+      "name": "Taschenrechner",
+      "description": "Grundrechenarten mit Tastatureingabe"
+    },
+    "favorites": {
+      "name": "Favoriten",
+      "description": "Schnellzugriff auf Links",
+      "loading": "Favoriten werden geladen...",
+      "empty": "Noch keine Favoriten.",
+      "addTitle": "Titel",
+      "addUrl": "URL",
+      "addButton": "Hinzufuegen",
+      "listView": "Liste",
+      "gridView": "Kacheln",
+      "editButton": "Favorit bearbeiten",
+      "deleteButton": "Favorit loeschen",
+      "saveButton": "Speichern",
+      "cancelButton": "Abbrechen",
+      "error": "Fehler beim Laden der Favoriten"
+    },
+    "link": {
+      "name": "Link",
+      "description": "Einzelner Schnellzugriff-Link"
+    },
+    "stopwatch": {
+      "name": "Stoppuhr",
+      "description": "Zeitmessung mit Rundenzeiten",
+      "start": "Start",
+      "stop": "Stop",
+      "reset": "Reset",
+      "lap": "Runde"
     }
   },
   "admin": {