Add networking layer and wire up v9 login flow with unit tests.

Introduce APIClient/AuthAPI, complete login with multi-account selection, and polish the login card UI with shadow and keyboard dismiss.

Co-authored-by: Cursor <cursoragent@cursor.com>

suixinkan/Features/Auth/API/AuthAPI.swift

@@ -0,0 +1,47 @@
+//
+//  AuthAPI.swift
+//  suixinkan
+//
+
+import Foundation
+
+@MainActor
+/// 登录认证 API，封装 config、v9 登录和账号选择相关接口。
+final class AuthAPI {
+    private let client: APIClient
+
+    /// 初始化登录 API，并注入共享网络客户端。
+    init(client: APIClient) {
+        self.client = client
+    }
+
+    /// 获取 App 配置，控制注册/验证码登录入口显隐。
+    func getAppConfig() async throws -> AppConfigResponse {
+        try await client.send(
+            APIRequest(method: .get, path: "/api/app/config")
+        )
+    }
+
+    /// 使用手机号和密码发起 v9 登录，返回临时 token 及可选账号列表。
+    func login(username: String, password: String) async throws -> V9AuthResponse {
+        try await client.send(
+            APIRequest(
+                method: .post,
+                path: "/api/app/v9/login",
+                body: LoginRequest(username: username, password: password)
+            )
+        )
+    }
+
+    /// 选择具体景区或门店账号，换取正式登录 token。
+    func setUser(_ request: SetUserRequest, tokenOverride: String? = nil) async throws -> V9AuthResponse {
+        try await client.send(
+            APIRequest(
+                method: .post,
+                path: "/api/app/v9/set-user",
+                body: request
+            ),
+            tokenOverride: tokenOverride
+        )
+    }
+}