feat: revocable read-only API keys for machine access

Integrations such as the Wabenhain shop sync no longer need a service
account with a password (and without MFA). An admin creates a key under
Verwaltung > Automatisierung > API-Schlüssel.

- Key format ack_<8>_<43>; only its SHA-256 hash is stored, the key is
  shown exactly once. Optional expiry, "last used" timestamp, revocation
  takes effect immediately; create/revoke are audit-logged without the key.
- A key is not a user: JwtAuthGuard sets request.apiKey, PermissionsGuard
  admits it only to routes whose permission is among its scopes and never
  to user-only routes. Scopes come from a short allowlist (shop-sync:read).
- Managing keys requires the new permission api-keys:manage.
- Keys are excluded from backups on purpose; a restore means issuing a new
  key.

Additive migration (new table).

Co-Authored-By: Claude Opus 5.5 (1M context) <[email protected]>

ApiCore-Backend/prisma/schema.prisma

@@ -111,10 +111,34 @@ model User {
   webhookSubscriptions  WebhookSubscription[]
   documents             Document[]
   honeyBatchRelocations HoneyBatchRelocation[]
+  apiKeys               ApiKey[]
 
   @@index([roleId])
 }
 
+// Schlüssel für Maschinen-Zugriffe (z. B. Wabenhain-Shop-Sync) statt eines
+// Service-Kontos mit Passwort. Gespeichert wird nur der SHA-256-Hash des
+// Schlüssels; der Klartext wird genau einmal bei der Erstellung angezeigt.
+// Ein Schlüssel ist kein Benutzer: er darf nur die Routen, deren
+// Berechtigung in `scopes` steht (siehe api-keys/api-key-scopes.ts).
+model ApiKey {
+  id              String    @id @default(cuid())
+  name            String
+  // Anfang des Schlüssels ("ack_ab12cd34") - zum Wiedererkennen in der
+  // Liste, ohne den Schlüssel selbst zu speichern.
+  prefix          String
+  keyHash         String    @unique
+  scopes          String[]
+  createdByUserId String?
+  createdByUser   User?     @relation(fields: [createdByUserId], references: [id])
+  createdAt       DateTime  @default(now())
+  lastUsedAt      DateTime?
+  expiresAt       DateTime?
+  revokedAt       DateTime?
+
+  @@index([revokedAt])
+}
+
 model RefreshToken {
   id        String    @id @default(cuid())
   userId    String