refactor: 用 EndpointFetchConfig 纯数据类替代 ORM 对象传递，统一上游模型缓存管理

- 引入 EndpointFetchConfig dataclass 替代直接传递 ProviderEndpoint ORM 对象，
  避免 DB session 关闭后 DetachedInstanceError
- 新增 build_format_to_config() 统一构建 api_format -> EndpointFetchConfig 映射
- KeyAllowedModelsDialog 改用 useUpstreamModelsCache composable 管理上游模型获取
- useUpstreamModelsCache 增加 error 字段透传部分格式获取失败的 warning
- 删除废弃的 queryProviderUpstreamModels API 函数
- ProviderCandidate 添加 __lt__ 方法支持排序比较

src/plugins/load_balancer/base.py

@@ -28,6 +28,16 @@ class ProviderCandidate:
         if self.metadata is None:
             self.metadata = {}
 
+    def __lt__(self, other: object) -> bool:
+        if not isinstance(other, ProviderCandidate):
+            return NotImplemented
+        # 优先级数字越大越优先，权重越大越优先
+        return (-self.priority, -self.weight, str(getattr(self.provider, "id", ""))) < (
+            -other.priority,
+            -other.weight,
+            str(getattr(other.provider, "id", "")),
+        )
+
 
 @dataclass
 class SelectionResult: