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-backend/src/freigabe/freigabe.service.ts

@@ -0,0 +1,106 @@
+import { Injectable, Logger } from '@nestjs/common';
+import { InjectRepository } from '@nestjs/typeorm';
+import { Repository } from 'typeorm';
+import { DocumentType } from '../database/entities/document-type.entity';
+import { PaperlessService } from '../paperless/paperless.service';
+
+const FREIGABE_FIELD_ID = 15;
+
+@Injectable()
+export class FreigabeService {
+  private readonly logger = new Logger(FreigabeService.name);
+
+  constructor(
+    @InjectRepository(DocumentType)
+    private readonly documentTypeRepo: Repository<DocumentType>,
+    private readonly paperlessService: PaperlessService,
+  ) {}
+
+  async getFreigabeDocuments(page: number, pageSize: number, nurNichtFreigegeben: boolean) {
+    const docTypes = await this.documentTypeRepo.find({
+      where: { FreigabeErforderlich: true as any },
+    });
+
+    if (docTypes.length === 0) {
+      return { count: 0, results: [] };
+    }
+
+    const docTypeIds = docTypes.map((dt) => dt.DocumentTypeId).join(',');
+
+    const params: Record<string, any> = {
+      page,
+      page_size: pageSize,
+      document_type__id__in: docTypeIds,
+      ordering: '-created',
+      truncate_content: true,
+    };
+
+    if (nurNichtFreigegeben) {
+      // Filter für Belege, bei denen Custom Field 15 nicht gesetzt ist
+      params[`custom_fields__field_id`] = FREIGABE_FIELD_ID;
+      params[`custom_fields__value__isnull`] = true;
+    }
+
+    try {
+      const result = await this.paperlessService.getDocuments(params);
+      return result;
+    } catch (err: any) {
+      // Fallback: Paperless unterstützt den custom_fields-Filter möglicherweise nicht
+      // In diesem Fall alle Belege laden und client-seitig filtern
+      this.logger.warn('custom_fields Filter nicht unterstützt, lade alle Belege und filtere lokal');
+      const fallbackParams: Record<string, any> = {
+        page: 1,
+        page_size: 9999,
+        document_type__id__in: docTypeIds,
+        ordering: '-created',
+        truncate_content: true,
+      };
+      const allDocs = await this.paperlessService.getDocuments(fallbackParams);
+      const results: any[] = allDocs.results ?? [];
+
+      if (nurNichtFreigegeben) {
+        const filtered = results.filter((doc: any) => {
+          const cf = (doc.custom_fields ?? []).find((f: any) => f.field === FREIGABE_FIELD_ID);
+          return !cf || cf.value === null || cf.value === '' || cf.value === undefined;
+        });
+        const start = (page - 1) * pageSize;
+        return {
+          count: filtered.length,
+          results: filtered.slice(start, start + pageSize),
+        };
+      }
+
+      const start = (page - 1) * pageSize;
+      return {
+        count: results.length,
+        results: results.slice(start, start + pageSize),
+      };
+    }
+  }
+
+  async setFreigabe(documentId: number, value: string | null) {
+    const doc = await this.paperlessService.getDocument(documentId);
+    const customFields: any[] = [...(doc.custom_fields ?? [])];
+
+    const existing = customFields.find((f: any) => f.field === FREIGABE_FIELD_ID);
+    if (existing) {
+      existing.value = value;
+    } else if (value !== null && value !== '') {
+      customFields.push({ field: FREIGABE_FIELD_ID, value });
+    }
+
+    await this.paperlessService.updateDocument(documentId, { custom_fields: customFields });
+    return { success: true };
+  }
+
+  async getFreigabeOptions(): Promise<{ id: string; label: string }[]> {
+    const fields = await this.paperlessService.getCustomFields();
+    const field = (fields as any[]).find((f: any) => f.id === FREIGABE_FIELD_ID);
+    if (!field) return [];
+
+    const options: string[] = field.extra_data?.select_options ?? [];
+    return options
+      .filter((o) => o !== null && o !== undefined && o !== '')
+      .map((o) => ({ id: o, label: o }));
+  }
+}