feat(email): add JMAP delivery transport

[hmans]

Summary

Adds an opt-in JMAP transactional-email transport while preserving SMTP as the default and fully compatible configuration.

• Adds email.transport = "smtp" | "jmap" and bearer-token JMAP configuration.
• Submits plaintext account-flow email through JMAP with secure session/API validation, identity and Drafts discovery, wildcard-identity support, and safe draft-cleanup handling.
• Documents SMTP/JMAP operator setup and records the behavior in FDR-029.

JMAP submission acceptance is treated as successful email submission; Chatto does not claim final recipient delivery or add an outbox/retry system.

Validation

• mise test-cli
• pnpm --dir apps/docs-website build
• mise license-check

Closes #1440.