[Docs Agent] Release of Docs Agent v 0.4.2.

[kyolee415]

What's changed:

• Enhanced tooling integration: Introduced the agent tools command for seamless integration with external tools via MCP.
• Core system updates: Significant updates were made to model, embedding, and RAG handling. This includes refactoring model creation, updating embedding models, adding Chroma backups, and supporting Gemini 2.5 multimodal models.
• Flexible task execution: Docs Agent tasks can now execute custom scripts directly using the new script function within runtask.
• Improved input handling: The CLI and task files now offer enhanced support for specifying multiple input files. Use either repeated --file flags or a --list_file flag pointing to a file list.

Description of the change

Refactoring and new features

Motivation

New features as part of Docs Agent roadmap

Type of change

Choose one: (Feature request)

Checklist

• [ X] I have performed a self-review of my code.
• [ X] I have added detailed comments to my code where applicable.
• [ X] I have verified that my change does not break existing code.
• [ X] My PR is based on the latest changes of the main branch (if unsure, please run git pull --rebase upstream main).
• [ X] I am familiar with the Google Style Guide for the language I have coded in.
• [ X] I have read through the Contributing Guide and signed the Contributor License Agreement.