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/models/input_modifier_utils.dart

@@ -0,0 +1,38 @@
+import 'package:flutter/services.dart';
+
+/// Returns true when a stale mobile one-shot Shift state should be released
+/// by replaying a tracked Shift key-down as a synthesized key-up.
+///
+/// This is only valid on mobile when Flutter's cached Shift state is still on
+/// (`cachedShiftPressed == true`) but the current hardware/raw event reports
+/// Shift as off (`actualShiftPressed == false`).
+///
+/// A tracked Shift key-down is required so the caller can safely synthesize the
+/// matching key-up. Both `shiftLeft` and `shiftRight` are excluded because the
+/// Shift key event itself must be processed first; otherwise we could release
+/// the tracked key while still handling the original Shift press/release.
+/// Callers should evaluate this only after their cached modifier state has been
+/// updated for the current event.
+///
+/// When this returns true, the caller logs a line like:
+/// `input: releasing stale mobile Shift before replaying tracked raw key-up`
+/// immediately before calling `_releaseTrackedRawShiftKeyEventIfNeeded()`.
+bool shouldReleaseStaleMobileShift({
+  required bool isMobile,
+  required bool cachedShiftPressed,
+  required bool actualShiftPressed,
+  required LogicalKeyboardKey logicalKey,
+  required bool hasTrackedShiftKeyDown,
+}) {
+  if (!isMobile || !cachedShiftPressed || actualShiftPressed) {
+    return false;
+  }
+  if (!hasTrackedShiftKeyDown) {
+    return false;
+  }
+  if (logicalKey == LogicalKeyboardKey.shiftLeft ||
+      logicalKey == LogicalKeyboardKey.shiftRight) {
+    return false;
+  }
+  return true;
+}