Function verify_commitment_signature 

pub fn verify_commitment_signature(c: &StorageCommitment) -> bool

Verify a commitment’s ML-DSA-65 signature against its embedded public key. Does NOT check the peer binding (BLAKE3(pubkey) == sender_peer_id) — callers that need it (the client, the node) check it separately so the same function serves both the “trust the embedded key” and “bind to a peer” uses.