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/Projects/API/ProjectAPI.swift

@@ -6,7 +6,7 @@
 //
 
 import Foundation
-import Observation
+import Combine
 
 /// 项目服务协议，抽象摄影师项目和店铺项目接口以便 ViewModel 测试替换。
 @MainActor
@@ -56,9 +56,8 @@ protocol ProjectServing {
 
 /// 项目 API，封装项目管理、店铺项目管理相关接口。
 @MainActor
-@Observable
 final class ProjectAPI: ProjectServing {
-    @ObservationIgnored private let client: APIClient
+    private let client: APIClient
 
     /// 初始化项目 API，并注入共享网络客户端。
     init(client: APIClient) {