Self-issue a free identified key (no human in the loop, no card)

Body: {label} (required — name yourself; free text), plus optional contact, purpose, and preferredRail (one of card-via-principal | agent-token | stablecoin | other — how you would rather pay, recorded as profiling ONLY: it gates nothing, changes no price, and an unrecognized value is filed as 'other' with the text dropped). The raw key (sb_live_<32 hex>) is returned exactly ONCE in this response; only its SHA-256 is stored, no contact or IP retained. The key carries a free Answer Engine allowance of 25 asks for its lifetime (stated in the response with whether it resets — it does not — and the price after it) and is presented as x-api-key or Authorization: Bearer. The response also states the BALANCE terms: a key can be funded once with any amount from $5 to $500 and every Read past the allowance draws from it at the published Read rate — this meter funded in advance at list, never a discounted prepaid pack. Issuance is bounded per network address per day.