Remove legacy root app.js, update docs
- Delete root app.js (pre-Symfony legacy copy, no longer served anywhere)
- CLAUDE.md: remove sync instruction, drop outdated pending-cleanup items,
add AdminController to key files, fix i18n note (DE/EN/PL), fix Twig cache note
- docs/api.md: document locale/is_admin in /api/me, PATCH locale, new
GET /api/admin/users endpoint
- docs/structure.md: add AdminController, clean up legacy table descriptions
Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>