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/Profile/API/ProfileAPI.swift

@@ -6,13 +6,12 @@
 //
 
 import Foundation
-import Observation
+import Combine
 
 @MainActor
-@Observable
 /// 个人信息 API，封装“我的”页面需要的用户资料和资料更新接口。
 final class ProfileAPI {
-    @ObservationIgnored private let client: APIClient
+    private let client: APIClient
 
     /// 初始化个人信息 API，并注入共享网络客户端。
     init(client: APIClient) {