Request a Lightning offer for a premium product

Also sells the developer API call packs (api_builder_30d, api_growth_30d, api_scale_30d, api_calls_10k — listed by GET /v1/developer/plans, never by /v1/premium/products; the top-up answers 409 PLAN_REQUIRED without an active plan, and every pack answers 404 PRODUCT_UNAVAILABLE while the developer API is dark). Answers a 402 Lightning offer for one of the three premium SKUs: a bolt11 invoice minted at the platform's receive address for the product's price plus a macaroon bound to that product and price. Nothing is written and no balance exists — pay the invoice from any Lightning wallet, then POST /v1/premium/redeem with the macaroon to apply the product. A retried offer is simply a second invoice the client may pay instead (the first stays unpaid and expires). No Idempotency-Key: the invoice's payment hash is the idempotency spine. Requires a fresh, non-banned/frozen account. Rate limited 10/min/user. Returns 404 while PREMIUM_ENABLED is off — the switch stops new offers only; already-purchased benefits and in-flight redeems keep working.