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-frontend/src/api/settings.ts

@@ -176,3 +176,19 @@ export const INBOX_ACTION_LABELS: Record<InboxActionType, string> = {
   EXPORT: 'Export (FTP/WebDAV)',
   PAPERLESS: 'In Paperless importieren',
 };
+
+export interface AgrarmonitorStatusData {
+  connected: boolean;
+  registriert: boolean | null;
+  freigeschaltet: boolean | null;
+  error?: string;
+}
+
+export const agrarmonitorApi = {
+  getStatus: () =>
+    api.get<AgrarmonitorStatusData>('/api/agrarmonitor/status').then((r) => r.data),
+  registerDevice: (pcName: string, agrarmonitorId: string) =>
+    api
+      .post<{ success: boolean; message: string }>('/api/agrarmonitor/register', { pcName, agrarmonitorId })
+      .then((r) => r.data),
+};