[task] Reorganize prerequisites into Must Have / Must Configure / Will Need Later

[github-actions]

Objective

Restructure the prerequisites section in Quick Start to separate critical requirements from items that will be set up later in the guide.

Context

The current prerequisites list is comprehensive but overwhelming for beginners. It mixes critical setup items with things that are configured in later steps (like the PAT), which creates confusion. Related to #4826.

Approach

1. Update prerequisites section in docs/src/content/docs/setup/quickstart.mdx

2. Replace the single bulleted list with three categorized sections:

   Must Have (before you start):

   • GitHub account
   • GitHub CLI (gh) installed and authenticated
   • A GitHub repository you have admin access to

   Must Configure (in your repository):

   • GitHub Actions enabled
   • Discussions enabled
   • Appropriate repository permissions

   Will Need Later (you'll set this up in Step 3):

   • Personal Access Token (PAT) with Copilot Requests permission

3. Use Starlight's callout/aside components to visually separate these categories

4. Add brief explanation of why this categorization helps: "This guide walks you through setup step-by-step, so you don't need everything upfront"

Files to Modify

• Update: docs/src/content/docs/setup/quickstart.mdx (prerequisites section)

Acceptance Criteria

• Prerequisites split into three clear categories
• Each category has appropriate heading and explanation
• Items are in correct categories (e.g., PAT in "Will Need Later")
• Visual formatting makes categories distinct
• Overall list is less overwhelming than current version
  Related to 📚 Documentation Noob Test Report - November 26, 2025 #4826

AI generated by Plan Command for discussion #4826