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/relative_mouse_accumulator.dart

@@ -0,0 +1,58 @@
+/// A small helper for accumulating fractional mouse deltas and emitting integer deltas.
+///
+/// Relative mouse mode uses integer deltas on the wire, but Flutter pointer deltas
+/// are doubles. This accumulator preserves sub-pixel movement by carrying the
+/// fractional remainder across events.
+class RelativeMouseDelta {
+  final int x;
+  final int y;
+
+  const RelativeMouseDelta(this.x, this.y);
+}
+
+/// Accumulates fractional mouse deltas and returns integer deltas when available.
+class RelativeMouseAccumulator {
+  double _fracX = 0.0;
+  double _fracY = 0.0;
+
+  /// Adds a delta and returns an integer delta when at least one axis reaches a
+  /// magnitude of 1px (after truncation towards zero).
+  ///
+  /// If [maxDelta] is > 0, the returned integer delta is clamped to
+  /// [-maxDelta, maxDelta] on each axis.
+  RelativeMouseDelta? add(
+    double dx,
+    double dy, {
+    required int maxDelta,
+  }) {
+    // Guard against misuse: negative maxDelta would silently disable clamping.
+    assert(maxDelta >= 0, 'maxDelta must be non-negative');
+
+    _fracX += dx;
+    _fracY += dy;
+
+    int intX = _fracX.truncate();
+    int intY = _fracY.truncate();
+
+    if (intX == 0 && intY == 0) {
+      return null;
+    }
+
+    // Clamp before subtracting so excess movement is preserved in the accumulator
+    // rather than being permanently discarded during spikes.
+    if (maxDelta > 0) {
+      intX = intX.clamp(-maxDelta, maxDelta);
+      intY = intY.clamp(-maxDelta, maxDelta);
+    }
+
+    _fracX -= intX;
+    _fracY -= intY;
+
+    return RelativeMouseDelta(intX, intY);
+  }
+
+  void reset() {
+    _fracX = 0.0;
+    _fracY = 0.0;
+  }
+}