[plan] Add GitHub CLI explanation to prerequisites section

[github-actions]

Objective

Add a brief explanation of what the GitHub CLI is in the prerequisites section to help absolute beginners.

Context

The documentation assumes users know what "GitHub CLI" is, but absolute beginners may not understand it's a command-line tool or where to get it.

Implementation

In the prerequisites section, change:

Before:

**GitHub CLI** - Required for installation

After:

**GitHub CLI** (`gh`) - A command-line tool for GitHub operations. [Install here](https://cli.github.com)

Files to Update

• docs/src/content/docs/guides/quick-start.md (prerequisites section)
• Any other pages that list prerequisites

Acceptance Criteria

• GitHub CLI is explained as a "command-line tool"
• Link to installation page (https://cli.github.com) included
• Command name (gh) is mentioned
• Explanation is concise (one sentence)

AI generated by Plan Command for discussion #7874