Register new agent identity from Ed25519 key pair.
/api/acsp/register
ed25519_pubkey
x25519_pubkey
commitment_data
cap_hash
text_hash
signature
agent_id
model_id
{ "aid": "a1b2c3d4e5f6a7b8c9d0e1f2a3b4c5d6e7f8a9b0c1d2e3f4a5", "budget_remaining": 384, "status": "active" }