fix: isolate WEB_UI_HOST env var in test and handle empty string

- Patch WEB_UI_HOST in test_web_defaults to avoid env leak
- Handle empty WEB_UI_HOST string in config (fall back to 127.0.0.1)

gateway/config.py

@@ -478,7 +478,7 @@ def _apply_env_overrides(config: GatewayConfig) -> None:
         config.platforms[Platform.WEB].enabled = True
         config.platforms[Platform.WEB].extra.update({
             "port": int(os.getenv("WEB_UI_PORT", "8765")),
-            "host": os.getenv("WEB_UI_HOST", "127.0.0.1"),
+            "host": os.getenv("WEB_UI_HOST", "") or "127.0.0.1",
             "token": os.getenv("WEB_UI_TOKEN", ""),
         })
 

tests/gateway/test_web.py

@@ -81,6 +81,7 @@ class TestConfigEnvOverrides(unittest.TestCase):
     @patch.dict(os.environ, {
         "WEB_UI_ENABLED": "true",
         "WEB_UI_TOKEN": "",
+        "WEB_UI_HOST": "",
     }, clear=False)
     def test_web_defaults(self):
         config = GatewayConfig()