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/Schedule/API/ScheduleAPI.swift

@@ -6,7 +6,7 @@
 //
 
 import Foundation
-import Observation
+import Combine
 
 /// 排班服务协议，抽象排班列表、新增、删除和可关联订单接口。
 @MainActor
@@ -29,9 +29,8 @@ protocol ScheduleServing {
 
 /// 排班 API，封装摄影师排班相关接口。
 @MainActor
-@Observable
 final class ScheduleAPI: ScheduleServing {
-    @ObservationIgnored private let client: APIClient
+    private let client: APIClient
 
     /// 初始化排班 API，并注入共享网络客户端。
     init(client: APIClient) {