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

res/rustdesk.desktop

@@ -0,0 +1,19 @@
+[Desktop Entry]
+Name=RustDesk
+GenericName=Remote Desktop
+Comment=Remote Desktop
+Exec=rustdesk %u
+Icon=rustdesk
+Terminal=false
+Type=Application
+StartupNotify=true
+Categories=Network;RemoteAccess;GTK;
+Keywords=internet;linux;dart;rust;remote-control;p2p;teamviewer;rust-lang;rdp;remote-desktop;vnc;
+Actions=new-window;
+StartupWMClass=rustdesk
+
+X-Desktop-File-Install-Version=0.23
+
+[Desktop Action new-window]
+Name=Open a New Window
+Exec=rustdesk %u