Add llms.txt file to insight docs (#5887)

---
title: "[SDK/Dashboard/Portal] Feature/Fix: Concise title for the changes"
---

If you did not copy the branch name from Linear, paste the issue tag here (format is TEAM-0000):

## Notes for the reviewer
Anything important to call out? Be sure to also clarify these in your comments.

## How to test
Unit tests, playground, etc.

<!-- start pr-codex -->

---

## PR-Codex overview
This PR focuses on enhancing the documentation and functionality related to `Agents & LLMs` within the `thirdweb Insight` API, including new links, improved examples, and standardized usage instructions for better integration with AI tools.

### Detailed summary
- Added a new link for `llms.txt` in `sidebar.tsx`.
- Updated documentation in `page.mdx` to clarify API usage for `Agents & LLMs`.
- Revised code examples to use template literals for dynamic values.
- Simplified `ChainId` type to a number.
- Enhanced error handling and response structure in API examples.
- Included detailed instructions on authentication and API endpoints.

> ✨ Ask PR-Codex anything about this PR by commenting with `/codex {your question}`

<!-- end pr-codex -->