Bare `ZOOM` had no dispatch arm — only the sub-keyword forms (ZOOM
EXTENTS/IN/OUT/WINDOW/…) were handled, so typing `ZOOM` fell through to
an unknown-command error. It now starts the interactive window zoom.
Add the missing Zoom Window ribbon button: the command existed but had no
tool()/icon, so it was reachable only by typing. Wire it into View ▸
Navigate with a new dashed-rectangle magnifier icon.
Closes#210
Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>