Needs testing on dev first before merging (and a review)
Enables the mlkem768x25519-sha256 hybrid key exchange by default, fixing the OpenSSH 'not using a post-quantum key exchange' warning on git push. Migrates host-key and auth APIs (russh-keys folded into russh::keys) and adds tests pinning the fingerprint contract, key extraction, and PQ kex.
> Needs testing on dev first before merging (and a review)
Enables the mlkem768x25519-sha256 hybrid key exchange by default, fixing the OpenSSH 'not using a post-quantum key exchange' warning on git push. Migrates host-key and auth APIs (russh-keys folded into russh::keys) and adds tests pinning the fingerprint contract, key extraction, and PQ kex.