Email the claim link to a human

Pending claim keys only (scope invite). 2 invites per claim; each recipient gets at most 1 invite per day. The note is plain text (max 280 chars) and checked by the abuse filter. Errors: 422 invalid_recipient / note_too_long / note_rejected / recipient_opted_out, 410 claim_claimed / claim_expired, 429 invite_limit / rate_limited, 503 classifier_unavailable (retry or send without a note).