feat(enclave): add network-bound wrapped root-key bootstrap

[samlaf]

Joining nodes now fetch the network root key through an attested ECDH/AES-GCM wrapping flow. The getWrappedRootKey RPC takes an opaque serialized RootKeyRequest and returns an opaque serialized RootKeyResponse.

A requester sends a fresh nonce, an ephemeral secp256k1 ECDH public key, and attestation evidence over root_key_request_binding(network_id, nonce, eph_pk). The responder verifies that evidence, wraps root_key to the requester's attested ephemeral key, and returns its own ephemeral public key, the wrapped root key, and evidence over root_key_response_binding(network_id, nonce, responder_eph_pk, wrapped).

Also derive network_id at enclave-server startup from the exact bytes of /run/seismic/conf/network-manifest.json and thread it through tx_io and root-key bootstrap bindings. The server fails fast if the manifest is missing or malformed.

Other changes:

• bind getAttestationEvidence to tx_io_binding(network_id, tx_io_pk, epoch 0)
• rename boot.share_root_key to getWrappedRootKey
• keep seismic-enclave free of seismic-attestation by using opaque Vec bodies for bootstrap RPC payloads
• add bootstrap/network unit tests
• update mock/server docs, tdx-init comments, and integration-test naming

Known follow-ups:

• replace the temporary permissive bootstrap measurement policy with a real allowlist/admission check
• add an attestation evidence v2 RPC returning AttestationExchangeMessage and route that endpoint through seismic-attestation
• split today's seismic-enclave common crate into narrower RPC/crypto/mock/ bootstrap-protocol/custodian-IPC crates