feat: Web Push für Logbuch-Eigner bei Crew-Sync

Benachrichtigt Owner optional per VAPID/Web Push, wenn Collaborators
Änderungen synchronisieren — ohne Klartext-Inhalte, mit Opt-in in den
Einstellungen, Custom Service Worker und Deep-Link zum Logbuch.

Co-authored-by: Cursor <cursoragent@cursor.com>

server/package.json

@@ -15,12 +15,14 @@
     "cors": "^2.8.5",
     "dotenv": "^16.4.5",
     "express": "^4.19.2",
-    "prisma": "^5.10.2"
+    "prisma": "^5.10.2",
+    "web-push": "^3.6.7"
   },
   "devDependencies": {
     "@types/cors": "^2.8.17",
     "@types/express": "^4.17.21",
     "@types/node": "^20.11.24",
+    "@types/web-push": "^3.6.4",
     "tsx": "^4.7.1",
     "typescript": "^5.3.3"
   }