Aligns tab behavior with browsers and editors: pressing the middle mouse
button on any closable tab in SortableTabsStrip closes it without going
through the visible close icon.
- onAuxClick handler triggers onClose when event.button === 1.
- onMouseDown preventDefault on middle button suppresses the browser's
autoscroll affordance.
- Both handlers no-op when the tab is not closable, keeping non-editor
tab strips (skills catalog, settings sections, etc.) untouched.
Roberto Bertó
76eef473aa