fix: use fixed port 8000 instead of $PORT variable

railway.json

@@ -5,7 +5,7 @@
     "dockerfilePath": "Dockerfile"
   },
   "deploy": {
-    "startCommand": "gunicorn -w 2 -b 0.0.0.0:$PORT --timeout 120 --chdir /flask main:app",
+    "startCommand": "gunicorn -w 2 -b 0.0.0.0:8000 --timeout 120 --chdir /flask main:app",
     "restartPolicyType": "ON_FAILURE",
     "restartPolicyMaxRetries": 10
   }