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/auth/api-keys.controller.ts

@@ -1,4 +1,12 @@
-import { Controller, Get, Post, Delete, Body, Param, UseGuards } from '@nestjs/common';
+import {
+  Controller,
+  Get,
+  Post,
+  Delete,
+  Body,
+  Param,
+  UseGuards,
+} from '@nestjs/common';
 import { ApiKeysService } from './api-keys.service';
 import { JwtAuthGuard } from './jwt-auth.guard';