chore(go): audit root package

Share one request, decode, and error path across the client, public
endpoints, and export download; align types with the Backend contract
and split types_api.go.

Claude-Session: https://claude.ai/code/session_01Agoc9bRVE9KL7mmWtey9Vq

operations.go

@@ -2,13 +2,10 @@ package elydora
 
 import "fmt"
 
-// GenesisChainHash is the initial chain hash for an agent's first operation.
-// It is the base64url encoding of 32 zero bytes, matching the backend.
+// GenesisChainHash is the base64url encoding of 32 zero bytes.
 const GenesisChainHash = "AAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAA"
 
-// CreateOperation builds a signed EOR from the given parameters.
-// It generates a UUIDv7 operation ID, a nonce, computes the payload hash and chain hash,
-// and signs the entire record with the client's private key.
+// CreateOperation builds and signs an EOR locally.
 func (c *Client) CreateOperation(params *CreateOperationParams) (*EOR, error) {
 	if params == nil {
 		return nil, fmt.Errorf("elydora: params must not be nil")