feat(backend): Benachrichtigungssystem (Modul 26)

NotificationsModule: Notification-Modell mit Prioritaeten INFO/
HINWEIS/WARNUNG/KRITISCH, GET /notifications (eigene + Broadcast),
POST /notifications/:id/read. record() als interne API fuer
kuenftige Automatisierungsregeln (Modul 30) vorgesehen.

ApiCore-Backend/src/app.module.ts

@@ -26,6 +26,7 @@ import { ProductsModule } from './products/products.module';
 import { BottlingModule } from './bottling/bottling.module';
 import { EquipmentModule } from './equipment/equipment.module';
 import { CalendarModule } from './calendar/calendar.module';
+import { NotificationsModule } from './notifications/notifications.module';
 import { JwtAuthGuard } from './auth/guards/jwt-auth.guard';
 import { RolesGuard } from './auth/guards/roles.guard';
 
@@ -57,6 +58,7 @@ import { RolesGuard } from './auth/guards/roles.guard';
     BottlingModule,
     EquipmentModule,
     CalendarModule,
+    NotificationsModule,
   ],
   controllers: [],
   providers: [