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/Core/Networking/APIEnvironment.swift

@@ -0,0 +1,60 @@
+//
+//  APIEnvironment.swift
+//  suixinkan
+//
+
+import Foundation
+
+/// 网络环境实体，集中描述 HTTP 和 WebSocket 的服务地址。
+struct APIEnvironment: Equatable {
+    let baseURL: URL
+    let webSocketURL: URL
+
+    nonisolated static let production = APIEnvironment(
+        baseURL: URL(string: "https://api.zhifly.cn")!,
+        webSocketURL: URL(string: "wss://api.zhifly.cn/wss")!
+    )
+
+    nonisolated static let testing = APIEnvironment(
+        baseURL: URL(string: "https://api-test.zhifly.cn")!,
+        webSocketURL: URL(string: "wss://api-test.zhifly.cn/wss")!
+    )
+
+    nonisolated static var current: APIEnvironment {
+        #if DEBUG
+        .testing
+        #else
+        .production
+        #endif
+    }
+}
+
+/// 客户端信息工具，负责提供网络请求所需的 App 版本和系统类型。
+enum AppClientInfo {
+    nonisolated static let osType = "iOS"
+
+    /// 生成后端要求的 App 版本号，版本号不足三段时用 build 号补齐。
+    nonisolated static func appVersion(infoDictionary: [String: Any]? = Bundle.main.infoDictionary) -> String {
+        let version = (infoDictionary?["CFBundleShortVersionString"] as? String)?
+            .trimmingCharacters(in: .whitespacesAndNewlines)
+            .nonEmpty ?? "1.0.0"
+        let build = (infoDictionary?["CFBundleVersion"] as? String)?
+            .trimmingCharacters(in: .whitespacesAndNewlines)
+            .nonEmpty
+        let versionParts = version.split(separator: ".", omittingEmptySubsequences: false)
+
+        if versionParts.count >= 3 {
+            return version
+        }
+        if versionParts.count == 2, let build {
+            return "\(version).\(build)"
+        }
+        return version
+    }
+}
+
+private extension String {
+    nonisolated var nonEmpty: String? {
+        isEmpty ? nil : self
+    }
+}