On mobile, the sidebar was 192px wide (w-48) and could appear collapsed (icons-only)
depending on prior desktop state. This introduces effectivelyCollapsed to always force
expanded mode when the mobile overlay is open, and uses a narrower w-40 (160px) width
to reduce screen coverage on small devices like iPhone SE (375px).
Co-Authored-By: Claude Sonnet 4.6 (1M context) <noreply@anthropic.com>