Folder query failures previously rendered identically to an empty
list, hiding network problems from the user. Add an isError branch
that shows "Failed to load folders." in destructive color.
Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>
Persistent left rail with "All documents" + "Root" pseudo-rows above
the tree. Each tree row has a chevron toggle (expand/collapse) and a
clickable label (select). Renders unlimited depth without blowing out
the page — children only mount when their parent is expanded.
Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>
