Screen one phone number for DNC + litigator status

DNC is free; a non-cached litigator lookup bills at $0.015. Requires an active payment method (HTTP 402 if not enabled). The screen NEVER rejects on a hit — the verdict is returned and the litigator/DNC badge is written to the contact profile; suppress flagged numbers downstream via the is_litigator audience filter. A recently-screened number returns the cached verdict (cached=true, no charge) unless force=true. A provider outage returns 503 with nothing billed — retry later. Sustained bursts beyond the per-account rate limit return 429 with a Retry-After header.

The Contact row is get-or-created (primary-acked) before screening — screen_litigator's caller contract — so the async consumer can persist the badge + usage row for numbers not yet on any list.