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/Account/API/AccountContextAPI.swift

@@ -6,7 +6,7 @@
 //
 
 import Foundation
-import Observation
+import Combine
 
 @MainActor
 /// 账号上下文服务协议，抽象权限、景区、门店和景点读取能力以便测试替换。
@@ -25,10 +25,9 @@ protocol AccountContextServing {
 }
 
 @MainActor
-@Observable
 /// 账号上下文 API，封装角色权限、景区、门店和景点读取接口。
 final class AccountContextAPI: AccountContextServing {
-    @ObservationIgnored private let client: APIClient
+    private let client: APIClient
 
     /// 初始化账号上下文 API，并注入共享网络客户端。
     init(client: APIClient) {