feat(08-04): LinkWidget implementation + page.tsx wiring (GREEN)

- LinkWidget: single-link widget reusing FavoriteLink backend (D-06)
- Single-link enforcement: add form hidden when link exists
- List (row) and tile (grid) view modes, switchable in edit mode
- Inline add/edit/delete forms in edit mode
- Letter fallback span + icon with onError hide (T-08-11)
- Links with target="_blank" rel="noreferrer" (T-08-12)
- i18n keys added to de.json + en.json (link.*)
- wireLinkWidget(LinkWidget) added to portal page.tsx
- All 7 link-widget tests pass (GREEN); tsc --noEmit clean

apps/web/src/messages/de.json

@@ -215,7 +215,19 @@
     },
     "link": {
       "name": "Link",
-      "description": "Einzelner Schnellzugriff-Link"
+      "description": "Einzelner Schnellzugriff-Link",
+      "loading": "Link wird geladen...",
+      "empty": "Noch kein Link gesetzt.",
+      "addTitle": "Titel",
+      "addUrl": "URL",
+      "addButton": "Hinzufuegen",
+      "listView": "Liste",
+      "gridView": "Kachel",
+      "editButton": "Link bearbeiten",
+      "deleteButton": "Link loeschen",
+      "saveButton": "Speichern",
+      "cancelButton": "Abbrechen",
+      "error": "Fehler beim Laden des Links"
     },
     "stopwatch": {
       "name": "Stoppuhr",