feat(网关): 接口4 改由网关本机直接调豆包视觉模型，不再代理到 worker

- gateway/app.py: 接口4 handler 改为直接调用 face_features 模块
- face_features.py: API Key 读取支持 gateway/config.json
- gateway/config.example.json: 增加 ark_api_key 配置项

face_features.py

@@ -55,17 +55,21 @@ _client = None
 
 
 def _load_api_key() -> str | None:
-    """ARK_API_KEY 环境变量优先，否则读 worker_config.json 的 ark_api_key。"""
+    """ARK_API_KEY 环境变量优先，否则读 worker_config.json / gateway/config.json 的 ark_api_key。"""
     key = os.getenv("ARK_API_KEY")
     if key:
         return key
-    cfg = os.path.join(os.path.dirname(__file__), "worker_config.json")
-    if os.path.isfile(cfg):
-        try:
-            with open(cfg, encoding="utf-8") as f:
-                return json.load(f).get("ark_api_key")
-        except Exception as e:  # noqa: BLE001
-            logger.warning("读取 worker_config.json ark_api_key 失败：%s", e)
+    base = os.path.dirname(__file__)
+    for cfg_name in ("worker_config.json", "gateway/config.json"):
+        cfg = os.path.join(base, cfg_name)
+        if os.path.isfile(cfg):
+            try:
+                with open(cfg, encoding="utf-8") as f:
+                    v = json.load(f).get("ark_api_key")
+                    if v:
+                        return v
+            except Exception as e:  # noqa: BLE001
+                logger.warning("读取 %s ark_api_key 失败：%s", cfg_name, e)
     return None