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/en.json

@@ -192,6 +192,38 @@
       "description": "Free-text notes with Markdown",
       "defaultTitle": "Note",
       "autosaveError": "Save failed"
+    },
+    "calculator": {
+      "name": "Calculator",
+      "description": "Basic arithmetic with keyboard support"
+    },
+    "favorites": {
+      "name": "Favorites",
+      "description": "Quick-access links",
+      "loading": "Loading favorites...",
+      "empty": "No favorites yet.",
+      "addTitle": "Title",
+      "addUrl": "URL",
+      "addButton": "Add",
+      "listView": "List",
+      "gridView": "Grid",
+      "editButton": "Edit favorite",
+      "deleteButton": "Delete favorite",
+      "saveButton": "Save",
+      "cancelButton": "Cancel",
+      "error": "Error loading favorites"
+    },
+    "link": {
+      "name": "Link",
+      "description": "Single quick-access link"
+    },
+    "stopwatch": {
+      "name": "Stopwatch",
+      "description": "Time measurement with lap times",
+      "start": "Start",
+      "stop": "Stop",
+      "reset": "Reset",
+      "lap": "Lap"
     }
   },
   "admin": {