feat(backend): Webhooks mit HMAC-signierter Auslieferung (Modul 28)

WebhooksModule (WebhookSubscription: URL, Events, Secret, aktiv) mit
Event-Dispatcher, angehaengt an 10 Ereignisse in 8 bestehenden Services
(colony.created, inspection.created, queen.created, queen.replaced,
harvest.created, batch.created, batch.updated, product.stock_changed,
task.created, task.completed). Auslieferung ist best-effort und blockiert
die ausloesende Anfrage nicht bei Fehlern.

ApiCore-Backend/src/app.module.ts

@@ -28,6 +28,7 @@ import { EquipmentModule } from './equipment/equipment.module';
 import { CalendarModule } from './calendar/calendar.module';
 import { NotificationsModule } from './notifications/notifications.module';
 import { StatisticsModule } from './statistics/statistics.module';
+import { WebhooksModule } from './webhooks/webhooks.module';
 import { JwtAuthGuard } from './auth/guards/jwt-auth.guard';
 import { RolesGuard } from './auth/guards/roles.guard';
 
@@ -61,6 +62,7 @@ import { RolesGuard } from './auth/guards/roles.guard';
     CalendarModule,
     NotificationsModule,
     StatisticsModule,
+    WebhooksModule,
   ],
   controllers: [],
   providers: [