Native Qt tooltips on macOS are unreliable (delayed or invisible). Replace
with a QFrame popup that appears on click, positioned below the ? button,
and closes when clicking elsewhere (Qt.Popup flag handles ESC and outside-click).
- Store help text in self._help_text instead of setToolTip()
- Add _toggle_help_popup() method: creates/destroys floating QFrame
- Update test to check _help_text attribute instead of toolTip()
Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>