优化配置，修复 demo bug

1，network 框架完善
2，websocket 机制完善
3，设计文档整理到架构文档
4，脚本，配置完善

apps/im_app/ios/Runner/AppDelegate.swift

@@ -1,8 +1,8 @@
-import Flutter
+@preconcurrency import Flutter
 import UIKit
 
 @main
-@objc class AppDelegate: FlutterAppDelegate, FlutterImplicitEngineDelegate {
+@objc class AppDelegate: FlutterAppDelegate {
 
   override func application(_ application: UIApplication, didFinishLaunchingWithOptions launchOptions: [UIApplication.LaunchOptionsKey: Any]?) -> Bool {
     return super.application(application, didFinishLaunchingWithOptions: launchOptions)
@@ -16,9 +16,11 @@ import UIKit
     sceneConfig.delegateClass = SceneDelegate.self
     return sceneConfig
   }
+}
 
-  // MARK: - FlutterImplicitEngineDelegate
-
+// FlutterImplicitEngineDelegate 来自 Flutter ObjC 框架，尚未标注 @MainActor，
+// 用 @preconcurrency 抑制 Swift 6 ConformanceIsolation 错误。
+extension AppDelegate: @preconcurrency FlutterImplicitEngineDelegate {
   func didInitializeImplicitFlutterEngine(_ engineBridge: FlutterImplicitEngineBridge) {
     GeneratedPluginRegistrant.register(with: engineBridge.pluginRegistry)
   }