API errors now surface server message instead of generic status text

Patch Changes

• 9a286fa: Read API error messages from the standardized nested error envelope. The API now returns { error: { code, type, message } }; the CLI was still reading a top-level body.message, so non-2xx responses surfaced a generic status text (e.g. "Bad Request") instead of the server's actual message. A new apiErrorMessage() reader pulls error.message (tolerating the legacy flat { message } body), restoring precise error output.