chore: apply ESLint auto-fix across entire backend

Reformats code style (line breaks, indentation, type annotations)
without changing logic. Also includes minor feature additions bundled
in the same lint run (stats service, user-settings groups, agrarmonitor
polling improvements).

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

paperless-backend/src/kontonummern/kontonummern.controller.ts

@@ -22,4 +22,3 @@ export class KontonummernController {
     return this.kontonummernService.create(dto.correspondentId, dto.nummer);
   }
 }
-