09cd1a5fe2
1. plugin_error_handler.py: Remove return_annotation from copied signature
to prevent FastAPI ForwardRef('UploadFile') resolution failure on routes
with file upload endpoints (dms, calendar, mail, kommunikation, ai_assistant)
2. middleware.py: Skip CSRF check for WebSocket upgrade requests
WebSocket connections use GET with upgrade header — should not be
blocked by CSRF middleware