refactor: add dynamic runtime settings compatibility proxy

app/runtime/settings.py

@@ -11,6 +11,24 @@ RuntimeSettingProvider = Callable[[str], Any]
 _provider: RuntimeSettingProvider | None = None
 
 
+class RuntimeSettingsCompat:
+    """为旧模块级 Settings 访问提供动态 runtime 配置代理。"""
+
+    def __getattr__(self, key: str) -> Any:
+        """读取当前组合根配置；未装配时沿用旧 Settings 回退。"""
+        return get_runtime_setting(key)
+
+    def __setattr__(self, key: str, value: Any) -> None:
+        """把旧模块级覆盖同步到 legacy Settings，保持测试和插件注入语义。"""
+        legacy_settings = importlib.import_module("app.runtime.config").settings
+        setattr(legacy_settings, key, value)
+
+    def __delattr__(self, key: str) -> None:
+        """删除旧模块级覆盖，使配置对象恢复其原有属性解析。"""
+        legacy_settings = importlib.import_module("app.runtime.config").settings
+        delattr(legacy_settings, key)
+
+
 def configure_runtime_setting_provider(provider: RuntimeSettingProvider) -> None:
     """由启动组合根登记配置读取器，保持适配器只依赖 runtime 端口。"""
     global _provider