Recapture all six README screenshots against the new sidebar nav,
subject-grouped library, and updated Settings / Canvas export UI.
Co-authored-by: Claude <claude-code@anthropic.com>
Replace top Nav with Sidebar, add lib/group.js for library grouping,
tokenized color/alert styles, and tighter Settings/Canvas export layout.
Adds @tabler/icons-react. Verified production build (standalone) passes,
so the Docker image built from this tree matches the local app.
Co-authored-by: Claude <claude-code@anthropic.com>
