Bilateral AI provenance standard adds agent self-signing to notarized records

A new cryptographic protocol called Bilateral Signature (v0x04) addresses a gap in AI output provenance by requiring an AI agent to sign its own work hash before an independent notary counter-signs it. Previously, the v0x03 standard only proved a hash existed at a given timestamp, but could not confirm the agent actually authored the underlying content. The updated protocol fuses the agent's Ed25519 signature into the notarized record, meaning any forgery would require compromising two separate private keys instead of one. The new version maintains the same 239-byte size, $0.01 cost, and binary layout as its predecessor, with the notary automatically selecting v0x04 when an agent signature is included in the request. All nine existing mainnet records under v0x03 remain valid without migration.