Initial commit: RustDesk 1.4.7 macOS desktop port

- Filled empty libs/hbb_common/ submodule (cloned from rustdesk/hbb_common)
- Patched Flutter 3.44 / Dart 3.12 compatibility:
  * flutter/lib/generated_bridge.dart: asTypedList with cast<>, DartPort=Int64
  * flutter/lib/common.dart: DialogTheme->DialogThemeData, TabBarTheme->TabBarThemeData
  * flutter/pubspec.yaml: extended_text 14.0.0->15.0.2, google_fonts override 5.0.0
  * flutter/macos/Runner/Configs/Release.xcconfig: EXCLUDED_ARCHS=x86_64
- Build verified: cargo check + cargo build --features flutter + cargo build --release --features flutter
- Verified flutter build macos --debug and --release both produce working .app
- Verified .dmg installer (27MB arm64) created via hdiutil
- Build deps: Xcode 26.5, CocoaPods 1.16.2, Flutter 3.44, VCPKG arm64-osx

flutter/lib/plugin/event.dart

@@ -0,0 +1,18 @@
+import 'dart:convert';
+import 'package:flutter/material.dart';
+
+void handlePluginEvent(
+  Map<String, dynamic> evt,
+  Function(Map<String, dynamic> e) handleMsgBox,
+) {
+  Map<String, dynamic>? content;
+  try {
+    content = json.decode(evt['content']);
+  } catch (e) {
+    debugPrint(
+        'Json decode plugin event content failed: $e, ${evt['content']}');
+  }
+  if (content?['t'] == 'MsgBox') {
+    handleMsgBox(content?['c']);
+  }
+}