README: what the webmail now does, the architecture roles, a short guide with the
shortcuts, testing with a real database, and an honest list of what is not
finished. New docs/WEBMAIL.md as the reference for each feature and for the
colour system. OPERATIONS: sessions and trusted senders. DEPLOYMENT: the
two-step release as API calls, and what to expect when upgrading. MAILBOX-CORE:
the conversation invariants and migrations 0015 to 0018.
Co-Authored-By: Claude Sonnet 5.5 <noreply@anthropic.com>
