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?
 

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

suixinkan/Features/Tasks/ViewModels/TaskManagementViewModel.swift

@@ -38,7 +38,7 @@ enum TaskStatusFilter: Int, CaseIterable, Identifiable {
 /// 任务管理 ViewModel，负责任务列表、筛选、分页和错误状态。
 @MainActor
 final class TaskManagementViewModel: ObservableObject {
-    @Published var isLoading = false
+    private var isLoading = false
     @Published var isLoadingMore = false
     @Published var tasks: [PhotographerTaskItem] = []
     @Published var total = 0
@@ -146,7 +146,7 @@ final class TaskManagementViewModel: ObservableObject {
 /// 任务详情 ViewModel，负责详情加载和列表摘要兜底展示。
 @MainActor
 final class TaskDetailViewModel: ObservableObject {
-    @Published var isLoading = false
+    private var isLoading = false
     @Published var detail: TaskDetailResponse?
     @Published var errorMessage: String?