v0.4.0 — Voice personas

Voice personas

Adds a documented pattern for learning how the user writes on each messaging
platform (Slack, email, WhatsApp, LinkedIn, Twitter/X) and drafting future
messages in that same voice.

• New: docs/routines/voice-personas.md
  — a routine that samples the user's own sent messages per platform, stores
  the derived style as a voice_persona brain entity (tone, structure,
  punctuation/emoji habits, openers/closers, vocabulary, audience-tagged
  register variants), and recalls it before drafting anything on that
  platform. Drafting always previews before send — never auto-sends.
• Generalizes the ad-hoc taste-slack-voice / whatsapp-voice skills: the
  brain becomes the source of truth for the voice itself, re-derivable and
  correctable rather than hand-maintained prose.
• README and docs/mcps.md now point to the new routine.

Docs-only release — no code or schema changes.