Fixes#241
When users set HONCHO_API_KEY via `hermes config set` or environment
variable, they expect the integration to activate. Previously, the
`enabled` flag defaulted to `false` when reading from global config,
requiring users to also explicitly enable Honcho.
This change auto-enables Honcho when:
- An API key is present (from config file or env var)
- AND `enabled` is not explicitly set to `false` in the config
Users who want to disable Honcho while keeping the API key can still
set `enabled: false` in their config.
Also adds unit tests for the auto-enable behavior.
