[ rhonda-rodododo/llamenos ] docs: update documentation for Epic 54 architecture changes

- Update CLAUDE.md with 6 DOs, messaging adapters, key management patterns
- Update DEVELOPMENT.md with PIN-encrypted key store, device linking, DO split details
- Update README.md with volunteer experience features, session management, 13 languages
- Add Epics 37-41 and 48-52 to completed backlog
- Add multi-provider telephony and volunteer experience sections to marketing site (en+es)

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>
https://github.com/rhonda-rodododo/llamenos/commit/f1f3bb3a3368f81b14874b029561fdf6a49e97c9