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/MessageCenter/ViewModels/MessageCenterViewModel.swift

@@ -6,22 +6,21 @@
 //
 
 import Foundation
-import Observation
+import Combine
 
 @MainActor
-@Observable
 /// 消息中心 ViewModel，负责消息分页、筛选、已读和删除。
-final class MessageCenterViewModel {
-    var messages: [MessageItem] = []
-    var selectedFilter: MessageFilter = .all
-    var isLoading = false
-    var isLoadingMore = false
-    var loadFailed = false
-    var loadFailureReason: String?
-    var message: String?
+final class MessageCenterViewModel: ObservableObject {
+    @Published var messages: [MessageItem] = []
+    @Published var selectedFilter: MessageFilter = .all
+    @Published var isLoading = false
+    @Published var isLoadingMore = false
+    @Published var loadFailed = false
+    @Published var loadFailureReason: String?
+    @Published var message: String?
 
-    private(set) var hasMoreMessages = false
-    private(set) var lastId = 0
+    @Published private(set) var hasMoreMessages = false
+    @Published private(set) var lastId = 0
     private let pageSize = 20
 
     /// 未读消息数量。