Build FolderTree component that renders the vault's directory
structure below the TYPES sections. Integrates with SidebarSelection
to filter the note list by folder path. Styled to match the
ui-design.pen "Folder Tree Sidebar" frame with Phosphor folder
icons, blue highlight for selected folder, and indented children
with guide lines. Wire folder data from useVaultLoader → App → Sidebar.
Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>
