fix: update health check URL to use dynamic backend port from settings

- Modified the health check request in app.py to utilize the BACKEND_PORT setting for improved configuration flexibility.

app.py

@@ -58,7 +58,7 @@ def check_backend_health() -> tuple[bool, str]:
     返回: (is_healthy, status_html)
     """
     try:
-        response = requests.get("http://localhost:8000/api/v1/health/", timeout=2)
+        response = requests.get(f"http://localhost:{settings.BACKEND_PORT}/api/v1/health/", timeout=2)
         if response.status_code == 200:
             data = response.json()
             if data.get("code") == 0: