The doc was from the initial commit and predated all open-item work. Update
the works-end-to-end list (protocol doc, away-fallthrough, mavcaldav,
quiet-hours schedule, tools enable/disable, note RAG, passkey step-up), rework
the not-built-yet ranking (at-rest crypto, mavweb/mavcaldav tests, systemd),
and add the rationale for deferring multi-user.
Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>