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/prisma/schema.prisma

@@ -20,6 +20,32 @@ model User {
   credentials              Credential[]
   logbooks                 Logbook[]
   collaborations           Collaboration[]
+  pushSubscriptions        PushSubscription[]
+  notificationPrefs        UserNotificationPrefs?
+}
+
+model PushSubscription {
+  id        String   @id @default(uuid())
+  userId    String
+  endpoint  String   @unique
+  p256dh    String
+  auth      String
+  userAgent String?
+  locale    String?
+  createdAt DateTime @default(now())
+  updatedAt DateTime @updatedAt
+
+  user User @relation(fields: [userId], references: [id], onDelete: Cascade)
+
+  @@index([userId])
+}
+
+model UserNotificationPrefs {
+  userId                     String   @id
+  collaboratorChangesEnabled Boolean  @default(false)
+  updatedAt                  DateTime @updatedAt
+
+  user User @relation(fields: [userId], references: [id], onDelete: Cascade)
 }
 
 model Credential {