fix(perm): set HOME env var in main.py to redirect gunicorn control files

backend/main.py

@@ -1,6 +1,10 @@
 import os
 # Fix matplotlib/gunicorn permission issues in server environment
-os.environ['MPLCONFIGDIR'] = os.path.join(os.getcwd(), 'temp')
+_temp_dir = os.path.join(os.getcwd(), 'temp')
+os.makedirs(_temp_dir, exist_ok=True)
+os.environ['MPLCONFIGDIR'] = _temp_dir
+os.environ['HOME'] = _temp_dir
+
 from fastapi import FastAPI, HTTPException, Request, WebSocket, WebSocketDisconnect, Query
 from fastapi.staticfiles import StaticFiles
 from fastapi.middleware.cors import CORSMiddleware