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/Invite/API/InviteAPI.swift

@@ -6,7 +6,7 @@
 //
 
 import Foundation
-import Observation
+import Combine
 
 /// 邀请服务协议，抽象邀请信息和邀请记录接口。
 @MainActor
@@ -20,9 +20,8 @@ protocol InviteServing {
 
 /// 邀请 API，封装摄影师邀请相关接口。
 @MainActor
-@Observable
 final class InviteAPI: InviteServing {
-    @ObservationIgnored private let client: APIClient
+    private let client: APIClient
 
     /// 初始化邀请 API，并注入共享网络客户端。
     init(client: APIClient) {