从 iOS 17 Observation 迁移至 iOS 16 兼容的 Combine 架构

将最低部署版本降至 iOS 16，以 ObservableObject 替换 @Observable，新增导航与 UI 兼容层，并补充登录冒烟 UI 测试。

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

suixinkan/Features/Tasks/ViewModels/TaskCreateViewModel.swift

@@ -6,7 +6,7 @@
 //
 
 import Foundation
-import Observation
+import Combine
 
 /// 任务云盘选择项实体，表示发布任务表单中的云盘附件。
 struct TaskCloudSelectionItem: Identifiable, Hashable {
@@ -43,19 +43,18 @@ struct TaskLocalUploadItem: Identifiable, Hashable {
 
 /// 发布任务 ViewModel，负责表单、附件上传和提交任务。
 @MainActor
-@Observable
-final class TaskCreateViewModel {
-    var taskName = ""
-    var remark = ""
-    var urgentHourText = "0"
-    var selectedOrder: AvailableOrderResponse?
-    var availableOrders: [AvailableOrderResponse] = []
-    var selectedCloudFiles: [TaskCloudSelectionItem] = []
-    var selectedLocalFiles: [TaskLocalUploadItem] = []
-    var isLoadingOrders = false
-    var isSubmitting = false
-    var errorMessage: String?
-    var didSubmitSuccessfully = false
+final class TaskCreateViewModel: ObservableObject {
+    @Published var taskName = ""
+    @Published var remark = ""
+    @Published var urgentHourText = "0"
+    @Published var selectedOrder: AvailableOrderResponse?
+    @Published var availableOrders: [AvailableOrderResponse] = []
+    @Published var selectedCloudFiles: [TaskCloudSelectionItem] = []
+    @Published var selectedLocalFiles: [TaskLocalUploadItem] = []
+    @Published var isLoadingOrders = false
+    @Published var isSubmitting = false
+    @Published var errorMessage: String?
+    @Published var didSubmitSuccessfully = false
 
     /// 判断当前表单是否满足提交按钮启用条件。
     var canSubmit: Bool {