Admin item/tag edit pages weren't rendering because TanStack Router treated them as children of the list route (which had no Outlet). Moving to directory-based routing (items/index.tsx + items/$itemId.tsx) makes them siblings that render directly in the admin layout. Also adds UAT results for phases 35-38 and backlog item 999.12 (Admin UX Polish). Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>