Press F9 in the viewer to toggle the menubar at the top of the
viewer. The menubar occupies the top row, and the viewer content
shifts down by 1 row when the menubar is open.
- Viewer::menubar: Option<ViewerMenuBar> field
- Viewer::render: calls mb.render() at the top when menubar is open
- Viewer::handle_key: F9 toggles, other keys route to menubar when open
- Viewer::execute_menubar_cmd: dispatches ViewerCmd to existing
viewer methods (ToggleHex, ToggleMagic, ToggleWrap, ToggleGrowing,
Search, SearchNext, SearchPrev, Goto)
Bookmark / file navigation / close commands are documented as a
planned follow-up — still reachable via their keyboard shortcuts.
Tests: 1393 pass, zero warnings.
vasilito
ae113df83c