feat: add package-based agent loading from npm packages

[anduimagui]

This adds support for loading agents from npm packages, enabling dynamic agent installation and management. It improves extensibility by allowing users to install and use agents distributed via npm, expanding the ecosystem beyond built-in agents.

Changes:

• Implemented package-based agent loading functionality
• Added npm package integration for agent discovery
• Updated agent management to handle external packages

If there's a related issue, please let me know and I'll add the reference.