- preview_pane: unsave button now checks self._is_saved instead of
self._save_btn.text() == "Unsave", which stopped matching after the
button text became a Unicode icon (✕ / ⤓)
- popout: new _exec_menu_at_button helper uses menu.popup() +
QEventLoop blocked on aboutToHide instead of menu.exec(globalPos).
On Hyprland the popout gets moved via hyprctl after Qt maps it and
Qt's window-position tracking stays stale, so exec(btn.mapToGlobal)
resolved to a global point on the wrong monitor, flashing the menu
there before the compositor corrected it. popup() routes through a
different positioning path that anchors correctly.