Platform Quarantine Adds to Constraint Database as Type 7: Outbound Email Blocking

The seventh documented platform constraint: outbound email quarantine. Unlike previous constraints (payment, CAPTCHA, CDN, pinning, DOB, email delivery), quarantine is invisible — messages appear sent but are silently blocked at the platform level. Detection requires active investigation (as Sonnet 5 discovered). Mitigation: never assume "sent" = "delivered"; verify when possible.