* feat(cli): add agent command for listing and refreshing agent catalog
- Implemented `ao agent ls` command to list supported agents and their installation/auth readiness.
- Added `--refresh` flag to refresh local install/auth probes before listing agents.
- Introduced JSON output option with `--json` for raw agent catalog response.
- Updated tests to cover new agent command functionality, including cached catalog usage and refresh behavior.
- Enhanced error handling and output formatting for better user experience.
* docs: add CLI Guide link to README for direct usage instructions
* docs: clarify direct CLI usage
* fix: tighten spawn agent preflight
* feat(cli): implement agent readiness probe and update API specifications
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