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/prisma/schema.prisma

@@ -52,6 +52,7 @@ model User {
   bottlingBatches    BottlingBatch[]
   notifications      Notification[]
   queenEvaluations   QueenEvaluation[]
+  webhookSubscriptions WebhookSubscription[]
 
   @@index([role])
 }
@@ -754,3 +755,21 @@ model Notification {
   @@index([userId, read])
   @@index([priority])
 }
+
+// ---------------------------------------------------------------------------
+// Webhooks (Abschnitt 27) – v1.x Modul 28
+// ---------------------------------------------------------------------------
+
+model WebhookSubscription {
+  id              String   @id @default(cuid())
+  url             String
+  events          String[]
+  secret          String
+  active          Boolean  @default(true)
+  createdByUserId String?
+  createdByUser   User?    @relation(fields: [createdByUserId], references: [id])
+  createdAt       DateTime @default(now())
+  updatedAt       DateTime @updatedAt
+
+  @@index([active])
+}