fix(macos): make fullscreen capture overlay configurable (#4622)

macOS showFullScreen() triggers a native fullscreen space transition
animation when capturing. Replace with show() using FramelessWindowHint,
WindowStaysOnTopHint, and Qt::Tool flags to avoid the animation.

Add a 'useNativeFullscreen' config option (default: off) so users who
prefer the native fullscreen behavior can re-enable it from
Settings > General.

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>