Cryptographic core for review

• PQXDH: Curve25519 + ML-KEM-768 hybrid • Double Ratchet, AES-256-GCM • CI builds + tests on Apple hardware • byte-for-byte conformance check vs Apple CryptoKit's ML-KEM-768

Source-available (review license, not OSI). Firebase backend, so some metadata exists — audit is honest about it.

github.com/VeilusDigital/PhantomChatCrypto

Audit: veilusdigital.co/audit

Critique welcome.