Verify any Duel Crash round. Randomness is a drand beacon "randomness" value (hex-encoded, decoded as UTF-8); HMAC-SHA256(serverSeed, `${randomness}:0`) → first 4 bytes as uint32 → crashPoint = max(1.0, (2^32 / (value + 1)) × 0.999) with a 0.1% house edge.
