feat: add Steuertags concept to separate workflow from content tags

- New steuertag_ids setting to mark tags as workflow-only (not editable)
- DocumentEditModal shows only content tags (non-Steuertags) as editable chips
- Backend preserves Steuertags when saving document tag changes
- ManuellBearbeitenPage renders content tag chips under document title
- New Steuertags settings tab with multi-select and color preview

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

paperless-backend/src/paperless/paperless.module.ts

@@ -9,6 +9,7 @@ import { DocumentField } from '../database/entities/document-field.entity';
 import { Task } from '../database/entities/task.entity';
 import { Document } from '../database/entities/document.entity';
 import { Attachment } from '../database/entities/attachment.entity';
+import { Setting } from '../database/entities/setting.entity';
 import { PostprocessingModule } from '../postprocessing/postprocessing.module';
 import { AuthModule } from '../auth/auth.module';
 
@@ -20,6 +21,7 @@ import { AuthModule } from '../auth/auth.module';
       Task,
       Document,
       Attachment,
+      Setting,
     ]),
     forwardRef(() => PostprocessingModule),
     AuthModule,