Update service ports in documentation and configuration files to 12000 for backend

frontend/app/config.py

@@ -4,6 +4,6 @@ import os
 
 class Config:
     SECRET_KEY = os.getenv("FLASK_SECRET_KEY", "dev-secret-change-in-production")
-    BACKEND_URL = os.getenv("BACKEND_URL", "http://localhost:8000")
+    BACKEND_URL = os.getenv("BACKEND_URL", "http://localhost:12000")
     SESSION_COOKIE_HTTPONLY = True
     SESSION_COOKIE_SAMESITE = "Lax"