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/common.dart

@@ -0,0 +1,42 @@
+import 'dart:convert';
+
+typedef PluginId = String;
+
+// ui location
+const String kLocationHostMainPlugin = 'host|main|settings|plugin';
+const String kLocationClientRemoteToolbarDisplay =
+    'client|remote|toolbar|display';
+
+class MsgFromUi {
+  String id;
+  String name;
+  String location;
+  String key;
+  String value;
+  String action;
+
+  MsgFromUi({
+    required this.id,
+    required this.name,
+    required this.location,
+    required this.key,
+    required this.value,
+    required this.action,
+  });
+
+  Map<String, dynamic> toJson() {
+    return <String, dynamic>{
+      'id': id,
+      'name': name,
+      'location': location,
+      'key': key,
+      'value': value,
+      'action': action,
+    };
+  }
+
+  @override
+  String toString() {
+    return jsonEncode(toJson());
+  }
+}