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/utils/scale.dart

@@ -0,0 +1,34 @@
+import 'package:flutter_hbb/consts.dart';
+import 'package:flutter_hbb/models/platform_model.dart';
+import 'package:uuid/uuid.dart';
+
+/// Clamp custom scale percent to supported bounds.
+/// Keep this in sync with the slider's minimum in the desktop toolbar UI.
+///
+/// This function exists to ensure consistent clamping behavior across the app
+/// and to provide a single point of reference for the valid scale range.
+int clampCustomScalePercent(int percent) {
+  return percent.clamp(kScaleCustomMinPercent, kScaleCustomMaxPercent);
+}
+
+/// Parse a string percent and clamp. Defaults to 100 when invalid.
+int parseCustomScalePercent(String? s, {int defaultPercent = 100}) {
+  final parsed = int.tryParse(s ?? '') ?? defaultPercent;
+  return clampCustomScalePercent(parsed);
+}
+
+/// Convert a percent value to scale factor after clamping.
+double percentToScale(int percent) => clampCustomScalePercent(percent) / 100.0;
+
+/// Fetch, parse and clamp the custom scale percent for a session.
+Future<int> getSessionCustomScalePercent(UuidValue sessionId) async {
+  final opt = await bind.sessionGetFlutterOption(
+      sessionId: sessionId, k: kCustomScalePercentKey);
+  return parseCustomScalePercent(opt);
+}
+
+/// Fetch and compute the custom scale factor for a session.
+Future<double> getSessionCustomScale(UuidValue sessionId) async {
+  final p = await getSessionCustomScalePercent(sessionId);
+  return percentToScale(p);
+}