feat: configure nginx proxy and response headers to support SSE for label print agent

paperless-backend/src/label-print-agent/label-print-agent.controller.ts

@@ -51,7 +51,8 @@ export class LabelPrintAgentController {
 
   // Agent: SSE-Stream für neue Druckaufträge
   @Sse('events')
-  sseEvents(): Observable<MessageEvent> {
+  sseEvents(@Res({ passthrough: true }) res: Response): Observable<MessageEvent> {
+    res.setHeader('X-Accel-Buffering', 'no');
     return this.service.newJob$.pipe(
       map(() => ({ data: { type: 'label-job-available' } } as MessageEvent)),
     );