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/email-download/zugferd.util.ts

@@ -1,8 +1,4 @@
-const KNOWN_NAMES = [
-  'factur-x.xml',
-  'zugferd-invoice.xml',
-  'xrechnung.xml',
-];
+const KNOWN_NAMES = ['factur-x.xml', 'zugferd-invoice.xml', 'xrechnung.xml'];
 
 export function isERechnung(pdfBuffer: Buffer): boolean {
   const asText = pdfBuffer.toString('latin1').toLowerCase();