feat: add Agrarmonitor integration module

- New backend module (agrarmonitor) with status check and device registration
- Frontend settings tab with connection status display and registration form
- Environment variables for base URLs, credentials, cookie path and encryption key
- Docker Compose env passthrough for agrarmonitor config

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

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

@@ -0,0 +1,22 @@
+import { Body, Controller, Get, HttpCode, Post } from '@nestjs/common';
+import { AgrarmonitorService } from './agrarmonitor.service';
+import { RequirePermissions } from '../auth/permissions.decorator';
+import { Permission } from '../auth/permissions.enum';
+
+@Controller('api/agrarmonitor')
+export class AgrarmonitorController {
+  constructor(private readonly service: AgrarmonitorService) {}
+
+  @Get('status')
+  @RequirePermissions(Permission.MANAGE_SETTINGS)
+  async getStatus() {
+    return this.service.getStatus();
+  }
+
+  @Post('register')
+  @HttpCode(200)
+  @RequirePermissions(Permission.MANAGE_SETTINGS)
+  async registerDevice(@Body() body: { pcName: string; agrarmonitorId: string }) {
+    return this.service.registerDevice(body.pcName, body.agrarmonitorId);
+  }
+}