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.service

@@ -0,0 +1,22 @@
+[Unit]
+Description=RustDesk
+Requires=network.target
+After=systemd-user-sessions.service
+
+[Service]
+Type=simple
+ExecStart=/usr/bin/rustdesk --service
+# kill --tray and --server both
+ExecStop=pkill -f "rustdesk --"
+# below two lines do not work, have to use above one line
+#ExecStop=pkill -f "rustdesk --tray"
+#ExecStop=pkill -f "rustdesk --server"
+PIDFile=/run/rustdesk.pid
+KillMode=mixed
+TimeoutStopSec=30
+User=root
+LimitNOFILE=100000
+Environment="PULSE_LATENCY_MSEC=60" "PIPEWIRE_LATENCY=1024/48000"
+
+[Install]
+WantedBy=multi-user.target