The sidebar had all categories expanded by default (collapsed: false),
which on mobile created a 60+ item flat list when opening the sidebar.
Reported by danny on Discord.
Changes:
- Set all top-level categories to collapsed: true (tap to expand)
- Enable autoCollapseCategories: true (accordion — opening one section
closes others, prevents the overwhelming flat list)
- Enable hideable sidebar (swipe-to-dismiss on mobile)
- Add mobile CSS: larger touch targets (0.75rem padding), bolder
category headers, visible subcategory indentation with left border,
wider sidebar (85vw / 360px max), darker backdrop overlay
bd376fe976