Add column ruler toggle to the viewer. Press Alt-R or use the
View F9 menu to toggle a ruler row showing column positions.
- Viewer::ruler: bool field (default false)
- Alt-R key binding toggles the ruler
- ViewerCmd::ToggleRuler + View menu entry in the menubar
- execute_menubar_cmd dispatches the toggle
Added 1 unit test verifying the toggle cycle (off→on→off).
Tests: 1419 pass (was 1418), zero warnings.
vasilito
9a0b2c5f4a