移除 MJRefresh 依赖，恢复 SwiftUI 系统下拉刷新。

同时收紧各 ViewModel 内部 isLoading 可见性，避免不必要的视图刷新。

Co-authored-by: Cursor <cursoragent@cursor.com>

suixinkan/Features/Tasks/ViewModels/TaskCreateViewModel.swift

@@ -51,7 +51,7 @@ final class TaskCreateViewModel: ObservableObject {
     @Published var availableOrders: [AvailableOrderResponse] = []
     @Published var selectedCloudFiles: [TaskCloudSelectionItem] = []
     @Published var selectedLocalFiles: [TaskLocalUploadItem] = []
-    @Published var isLoadingOrders = false
+    private(set) var isLoadingOrders = false
     @Published var isSubmitting = false
     @Published var errorMessage: String?
     @Published var didSubmitSuccessfully = false