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/Statistics/ViewModels/StatisticsViewModel.swift

@@ -6,21 +6,20 @@
 //
 
 import Foundation
-import Observation
+import Combine
 
 @MainActor
-@Observable
 /// 数据统计页面 ViewModel，管理时间段、汇总数据、每日明细和分页状态。
-final class StatisticsViewModel {
-    var selectedPeriod: StatisticsPeriod = .today
-    private(set) var loading = false
-    private(set) var loadingMore = false
-    private(set) var summary = StatisticsSummaryResponse()
-    private(set) var dailyItems: [StatisticsDailyItem] = []
-    private(set) var totalDailyCount = 0
-    private(set) var lastRefreshAt: Date?
+final class StatisticsViewModel: ObservableObject {
+    @Published var selectedPeriod: StatisticsPeriod = .today
+    @Published private(set) var loading = false
+    @Published private(set) var loadingMore = false
+    @Published private(set) var summary = StatisticsSummaryResponse()
+    @Published private(set) var dailyItems: [StatisticsDailyItem] = []
+    @Published private(set) var totalDailyCount = 0
+    @Published private(set) var lastRefreshAt: Date?
 
-    private var page = 1
+    @Published private var page = 1
     private let pageSize = 15
 
     /// 当前日数据是否还有下一页。