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

libs/hbb_common/examples/system_message.rs

@@ -0,0 +1,20 @@
+extern crate hbb_common;
+#[cfg(target_os = "linux")]
+use hbb_common::platform::linux;
+#[cfg(target_os = "macos")]
+use hbb_common::platform::macos;
+
+fn main() {
+    #[cfg(target_os = "linux")]
+    let res = linux::system_message("test title", "test message", true);
+    #[cfg(target_os = "macos")]
+    let res = macos::alert(
+        "System Preferences".to_owned(),
+        "warning".to_owned(),
+        "test title".to_owned(),
+        "test message".to_owned(),
+        ["Ok".to_owned()].to_vec(),
+    );
+    #[cfg(any(target_os = "linux", target_os = "macos"))]
+    println!("result {:?}", &res);
+}