feat: implement Freigabesystem for payment approval workflow

Adds a dedicated approval view for PM_Freigabe users to release documents
for payment by setting Paperless custom field 15 to a predefined value.

- Backend: VIEW_FREIGABE permission mapped to PM_Freigabe OIDC group
- Backend: FreigabeErforderlich flag on DocumentType entity (auto-migrated)
- Backend: FreigabeModule with endpoints to list documents, fetch field
  options dynamically from Paperless, and set the approval custom field
- Frontend: /freigabe route with filter (default: nicht freigegeben),
  paginated table, and modal to select approval value
- Frontend: Settings checkbox to mark document types as requiring approval
- Frontend: Freigabe menu item visible only to PM_Freigabe/PM_Admin users

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

paperless-frontend/src/api/freigabe.ts

@@ -0,0 +1,40 @@
+import api from './client';
+
+export interface FreigabeDocument {
+  id: number;
+  title: string;
+  created: string;
+  created_date: string;
+  correspondent: number | null;
+  document_type: number | null;
+  archive_serial_number: number | null;
+  tags: number[];
+  custom_fields: { field: number; value: any }[];
+}
+
+export interface FreigabeOption {
+  id: string;
+  label: string;
+}
+
+export interface FreigabeResult {
+  count: number;
+  results: FreigabeDocument[];
+}
+
+export const freigabeApi = {
+  getDocuments: (page = 1, pageSize = 25, nurNichtFreigegeben = true) =>
+    api
+      .get<FreigabeResult>('/api/freigabe/documents', {
+        params: { page, pageSize, nurNichtFreigegeben },
+      })
+      .then((r) => r.data),
+
+  setFreigabe: (docId: number, value: string | null) =>
+    api
+      .put<{ success: boolean }>(`/api/freigabe/documents/${docId}/freigabe`, { value })
+      .then((r) => r.data),
+
+  getOptions: () =>
+    api.get<FreigabeOption[]>('/api/freigabe/options').then((r) => r.data),
+};

paperless-frontend/src/api/settings.ts

@@ -6,6 +6,7 @@ export interface SettingDocType {
   TitelTemplate: string;
   TagNotReady: number | null;
   TagReady: number | null;
+  FreigabeErforderlich?: boolean | null;
 }
 
 export interface SettingDocField {