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/database/entities/content.entity.ts

@@ -1,4 +1,11 @@
-import { Entity, PrimaryGeneratedColumn, Column, OneToOne, JoinColumn, Index } from 'typeorm';
+import {
+  Entity,
+  PrimaryGeneratedColumn,
+  Column,
+  OneToOne,
+  JoinColumn,
+  Index,
+} from 'typeorm';
 import { Attachment } from './attachment.entity';
 
 @Entity('Contents')