chore: remove .agent folder and clean up CLAUDE.md

- Delete .agent/ documentation folder (unused)
- Simplify CLAUDE.md from 370 to ~90 lines
- Remove stale docs (HEALTHCHECK.md, IMPLEMENTATION_SUMMARY.md, TOON_INTEGRATION_SUMMARY.md)

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

Author: FrancescoSaverioZuppichini