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/Features/ScenicPermission/API/ScenicPermissionAPI.swift

@@ -6,7 +6,7 @@
 //
 
 import Foundation
-import Observation
+import Combine
 
 /// 景区权限模块服务协议，定义景区选择、权限申请和景区申请所需接口。
 @MainActor
@@ -34,10 +34,9 @@ protocol ScenicPermissionServing {
 }
 
 @MainActor
-@Observable
 /// 景区权限 API，封装景区选择和申请相关网络请求。
 final class ScenicPermissionAPI {
-    @ObservationIgnored private let client: APIClient
+    private let client: APIClient
 
     /// 初始化景区权限 API，并注入共享网络客户端。
     init(client: APIClient) {