feat(view): zoom-window ribbon button and bare ZOOM command

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>

src/modules/view/mod.rs

@@ -60,6 +60,7 @@ impl CadModule for ViewModule {
                 title: "Navigate",
                 tools: vec![
                     RibbonItem::LargeTool(zoom_ext::tool()),
+                    RibbonItem::Tool(zoom_window::tool()),
                     RibbonItem::Tool(zoom_in::tool()),
                     RibbonItem::Tool(zoom_out::tool()),
                     RibbonItem::Tool(pan::tool()),