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/src/auth/permissions/permission-catalog.ts

@@ -315,6 +315,12 @@ export const PERMISSION_CATALOG = [
     [['read', 'Freigegebene Daten für den Shop lesen']],
     3300,
   ),
+  ...group(
+    'API-Schlüssel',
+    'api-keys',
+    [['manage', 'Anlegen, ansehen und widerrufen']],
+    3400,
+  ),
 ] as const satisfies readonly PermissionCatalogEntry[];
 
 export type PermissionKey = (typeof PERMISSION_CATALOG)[number]['key'];