feat(sprint7): Phase 1 — notifications enhancement + push infrastructure

Phase 1 (Notification Enhancement):
- Extended NotificationType enum (ADMIN_MESSAGE, INFO_BOARD_POST, FORUM_REPLY, FORUM_MENTION)
- Extended StaffPermission enum (SEND_NOTIFICATIONS, MANAGE_INFO_BOARD, MODERATE_FORUM)
- Extended AuditEventType with Sprint 7 events
- Flyway V11: notification_sends + notification_send_recipients tables
- NotificationSend + NotificationSendRecipient entities
- NotificationSendRepository + NotificationSendRecipientRepository
- Extended NotificationService with sendBroadcast() and sendToSelected()
- NotificationComposeController (POST /compose, GET /sends)
- ComposeNotificationRequest DTO

Phase 1B (Push Infrastructure):
- Flyway V12: device_tokens + notification_preferences tables
- DeviceToken entity + DevicePlatform enum
- NotificationPreference entity + NotificationChannel enum
- DeviceTokenRepository + NotificationPreferenceRepository
- DeviceRegistrationService (register/unregister/list devices, max 10 per user)
- NotificationPreferenceService (get/create defaults, update, IN_APP always on)
- NotificationDispatchService (multi-channel fan-out: WebSocket, Web Push, FCM, Email)
- WebPushSender (VAPID-based, simplified for MVP)
- FcmPushSender (graceful degradation if not configured)
- PushPayload DTO
- DeviceRegistrationController (POST/GET/DELETE /devices, GET /vapid-key)
- NotificationPreferenceController (GET/PUT /preferences)
- ConsentType extended (NOTIFICATION_PUSH, NOTIFICATION_EMAIL)
- TargetType enum (ALL, SELECTED)

Frontend:
- Updated sw.js with push event handler + notification click handler
- push-subscription.ts (subscribeToPush, unsubscribe, permission helpers)
- notification-compose.ts service (compose, sends, devices, preferences APIs)
- i18n keys (de.json + en.json) for compose, preferences, push, devices

Configuration:
- application-docker.properties: VAPID + FCM push config properties
- MemberRepository: added findAllActiveUserIds() for broadcast

cannamanage-frontend/messages/de.json

@@ -499,7 +499,52 @@
       "QUOTA_WARNING": "Kontingent-Warnung",
       "BATCH_RECALLED": "Chargen-Rückruf",
       "DISTRIBUTION_RECORDED": "Ausgabe erfasst",
-      "SUBSCRIPTION_EXPIRING": "Abo läuft bald ab"
+      "SUBSCRIPTION_EXPIRING": "Abo läuft bald ab",
+      "ADMIN_MESSAGE": "Vereins-Nachricht",
+      "INFO_BOARD_POST": "Neuer Aushang",
+      "FORUM_REPLY": "Forum-Antwort",
+      "FORUM_MENTION": "Forum-Erwähnung"
+    },
+    "compose": {
+      "title": "Benachrichtigung verfassen",
+      "titleField": "Titel",
+      "messageField": "Nachricht",
+      "linkField": "Link (optional)",
+      "targetAll": "Alle Mitglieder",
+      "targetSelected": "Ausgewählte Mitglieder",
+      "selectMembers": "Mitglieder auswählen",
+      "send": "Senden",
+      "sending": "Wird gesendet...",
+      "sent": "Benachrichtigung gesendet an {count} Mitglieder",
+      "history": "Verlauf",
+      "sentAt": "Gesendet am",
+      "recipients": "Empfänger",
+      "readCount": "Gelesen"
+    },
+    "preferences": {
+      "title": "Benachrichtigungs-Einstellungen",
+      "inApp": "In-App (immer aktiv)",
+      "email": "E-Mail",
+      "webPush": "Browser Push-Benachrichtigungen",
+      "mobilePush": "Mobile Push-Benachrichtigungen",
+      "enabled": "Aktiviert",
+      "disabled": "Deaktiviert"
+    },
+    "push": {
+      "promptTitle": "Push-Benachrichtigungen aktivieren?",
+      "promptBody": "Erhalte Benachrichtigungen über Ausgaben, Events und Vereins-News direkt auf dein Gerät.",
+      "accept": "Aktivieren",
+      "decline": "Nicht jetzt",
+      "granted": "Push-Benachrichtigungen aktiviert",
+      "denied": "Push-Benachrichtigungen abgelehnt"
+    },
+    "devices": {
+      "title": "Registrierte Geräte",
+      "noDevices": "Keine Geräte registriert",
+      "remove": "Entfernen",
+      "web": "Web-Browser",
+      "ios": "iPhone/iPad",
+      "android": "Android-Gerät"
     }
   },
   "pwa": {