NIP-01 event canonicalization

The signing input is the serialized canonical form of the event template ([0, pubkey, created_at, kind, tags, content]). The event id is the SHA-256 of that serialization; the signature is BIP-340 Schnorr over secp256k1 with the signer public key.

Test vectors live in nSealr/specs under vectors/. The companion verifies every signed response against the same fixtures before accepting device output.