Migrate from iOS 17 Observation to iOS 16-compatible Combine architecture.

Lower deployment target to iOS 16, replace @Observable with ObservableObject, add navigation and UI compatibility shims, and include login smoke UI tests.

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

suixinkan/App/Navigation/NavigationRouter.swift

@@ -5,7 +5,7 @@
 //  Created by Codex on 2026/6/18.
 //
 
-import Observation
+import Combine
 import SwiftUI
 
 /// 应用内可导航目标，承载各 Tab 内部的路由目的地。
@@ -60,10 +60,9 @@ extension OrdersRoute {
 }
 
 @MainActor
-@Observable
 /// 单个 NavigationStack 的路径容器，用于保存某个 Tab 的导航历史。
-final class RouterPath {
-    var path: [AppRoute] = []
+final class RouterPath: ObservableObject {
+    @Published var path: [AppRoute] = []
 
     /// 将指定路由压入当前 Tab 的导航栈。
     func navigate(to route: AppRoute) {
@@ -77,13 +76,12 @@ final class RouterPath {
 }
 
 @MainActor
-@Observable
 /// 主导航状态中心，管理当前 Tab 和每个 Tab 独立的 NavigationStack 路径。
-final class AppRouter {
-    var selectedTab: AppTab = .home
-    var selectedOrdersEntry: OrdersEntry = .storeOrders
-    private(set) var pendingOrderScanCode: String?
-    private var routers: [AppTab: RouterPath] = [:]
+final class AppRouter: ObservableObject {
+    @Published var selectedTab: AppTab = .home
+    @Published var selectedOrdersEntry: OrdersEntry = .storeOrders
+    @Published private(set) var pendingOrderScanCode: String?
+    @Published private var routers: [AppTab: RouterPath] = [:]
 
     /// 获取指定 Tab 对应的路由路径容器，不存在时自动创建。
     func router(for tab: AppTab) -> RouterPath {