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

exports.go

@@ -1,9 +1,7 @@
 package elydora
 
 import (
-	"encoding/json"
 	"fmt"
-	"io"
 	"net/http"
 )
 
@@ -36,44 +34,20 @@ func (c *Client) GetExport(exportID string) (*GetExportResponse, error) {
 
 // DownloadExport downloads the raw file data for a completed export.
 func (c *Client) DownloadExport(exportID string) ([]byte, error) {
-	u := c.baseURL + fmt.Sprintf("/v1/exports/%s/download", exportID)
-
-	req, err := http.NewRequest(http.MethodGet, u, nil)
+	req, err := newRequest(http.MethodGet, c.baseURL+fmt.Sprintf("/v1/exports/%s/download", exportID), nil, c.token, "")
 	if err != nil {
-		return nil, fmt.Errorf("elydora: create request: %w", err)
+		return nil, err
 	}
-	if c.token != "" {
-		req.Header.Set("Authorization", "Bearer "+c.token)
-	}
-
 	resp, err := c.httpClient.Do(req)
 	if err != nil {
 		return nil, fmt.Errorf("elydora: http request: %w", err)
 	}
-	defer resp.Body.Close()
-
-	body, err := io.ReadAll(resp.Body)
+	body, err := readBody(resp, 0)
 	if err != nil {
-		return nil, fmt.Errorf("elydora: read response body: %w", err)
+		return nil, err
 	}
-
 	if resp.StatusCode < 200 || resp.StatusCode >= 300 {
-		var errResp errorResponse
-		if jsonErr := json.Unmarshal(body, &errResp); jsonErr == nil && errResp.Error.Code != "" {
-			return nil, &ElydoraError{
-				StatusCode: resp.StatusCode,
-				Code:       errResp.Error.Code,
-				Message:    errResp.Error.Message,
-				RequestID:  errResp.Error.RequestID,
-				Details:    errResp.Error.Details,
-			}
-		}
-		return nil, &ElydoraError{
-			StatusCode: resp.StatusCode,
-			Code:       ErrorCodeInternalError,
-			Message:    string(body),
-		}
+		return nil, apiError(resp.StatusCode, body)
 	}
-
 	return body, nil
 }