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/native/common.dart

@@ -0,0 +1,17 @@
+import 'dart:io';
+
+final isAndroid_ = Platform.isAndroid;
+final isIOS_ = Platform.isIOS;
+final isWindows_ = Platform.isWindows;
+final isMacOS_ = Platform.isMacOS;
+final isLinux_ = Platform.isLinux;
+final isWeb_ = false;
+final isWebDesktop_ = false;
+
+final isDesktop_ = Platform.isWindows || Platform.isMacOS || Platform.isLinux;
+
+String get screenInfo_ => '';
+
+final isWebOnWindows_ = false;
+final isWebOnLinux_ = false;
+final isWebOnMacOS_ = false;