HonchoClientConfig.from_env() set enabled=True unconditionally,
even when HONCHO_API_KEY was not set. When ~/.honcho/config.json
didn't exist, from_global_config() fell back to from_env() and
returned enabled=True with a null api_key, causing the Honcho
session indicator to display on every CLI launch.
Fix: from_env() now sets enabled=bool(api_key), matching the
auto-enable logic already used in from_global_config().
Also added api_key guard to the CLI display as defense-in-depth.