SMTP-verify specific contacts (SPENDS TOKENS)

Verifies the mailboxes of named person ids. Included in every plan at no charge; a re-check inside 90 days returns the cached verdict. Runs as a job, poll GET /api/verification/job/{jobId}. Rate limit: 30,000 ids a minute on Growth, up to 150,000 on Agency: batch ids into one call rather than looping.