Refine and Integrate GitHub CLI Guide

This is a follow-up to the excellent "GitHub CLI Setup" guide created in PR #7384. The goal is to better integrate the guide into the project's structure and learning portal, and to enhance it with a more convenient way to manage the GH_TOKEN.

This is a great task for learning how documentation is structured and rendered within the Neo.mjs project.

Tasks:

1. Move the Guide: The guide is currently located at learn/guides/development/GitHubCLISetup.md. Please move it to learn/guides/ai/GitHubCLISetup.md to group it with other AI-related guides.

2. Add to Learning Portal Navigation: To make the guide visible in the website's learning portal, add an entry for it in the learn/tree.json file. It should be placed under the "AI" section ("parentId": "guides/ai"). The entry should look something like this:

       {"name": "GitHub CLI Setup", "parentId": "guides/ai", "id": "guides/ai/GitHubCLISetup"}

3. Update Guide with .env Instructions: The current guide explains how to set the GH_TOKEN using export. A more convenient and persistent method is to use the project's .env file, which is already used for the GEMINI_API_KEY. Please add a new section to the guide explaining how to add the GH_TOKEN to the .env file (which is git-ignored for security).

   Example content to add:

   Using the .env File (Recommended)

   For a more permanent setup, you can add your token to the .env file located at the root of the project. This file is git-ignored, so your token will not be committed. If the file doesn't exist, you can create it.

   # .env
   GEMINI_API_KEY="your_gemini_key_here"
   GH_TOKEN="your_fine_grained_token_here"
   

   The npm run server-start command will automatically load these variables.

4. Update AGENTS.md Reference: The AGENTS.md file contains a reference to the guide's old location. Please update it to point to the new path: learn/guides/ai/GitHubCLISetup.md.

Verification:

After making the changes, you can verify them by:

1. Running npm run server-start.
2. Navigating to the portal app (http://localhost:8080/apps/portal/).
3. Finding the "GitHub CLI Setup" guide in the "Guides" -> "AI" section of the side navigation and checking that your new content is there.