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/TaskCloudFileSelectionViewModel.swift

@@ -39,7 +39,7 @@ final class TaskCloudFileSelectionViewModel: ObservableObject {
     @Published var searchText = ""
     @Published var selectedFilter: TaskCloudFileFilter = .all
     @Published var selectedFiles: [CloudDriveFile] = []
-    @Published var isLoading = false
+    private var isLoading = false
     @Published var isLoadingMore = false
     @Published var errorMessage: String?