Add comprehensive GitHub Copilot instructions for heads-wiki development

[Copilot]

This PR adds a comprehensive .github/copilot-instructions.md file that provides GitHub Copilot with detailed instructions on how to work effectively with the heads-wiki Jekyll documentation site.

What's Included

The instructions cover all essential aspects of working with this repository:

Setup and Build Process:

• Complete dependency installation (Ruby, Jekyll, just-the-docs theme)
• Exact build commands with validated timing expectations (~1.4 seconds)
• Local development server setup using local_config.yml

Repository Structure:

• Detailed breakdown of the 34 Markdown files across directories
• Explanation of Jekyll front matter and navigation system
• Configuration file differences between local and production

Validation Scenarios:

• Required manual testing steps after making changes
• End-to-end scenarios for adding new documentation
• Navigation and rendering verification procedures

Common Development Tasks:

• Adding new documentation with proper Jekyll front matter
• Modifying existing content while maintaining structure
• Working with images and assets

Important Notes:

• No CI/testing infrastructure exists - validation is entirely manual
• Sass deprecation warnings are expected and cosmetic
• Theme customization guidelines and deployment information

Validation

All instructions have been thoroughly tested end-to-end, including:

• Fresh installation and setup process
• Build timing measurements (consistently ~1.4 seconds)
• Site serving and functionality verification
• Adding new documentation and confirming it appears correctly
• Manual validation scenarios

The instructions follow the specified format with imperative tone and include explicit "NEVER CANCEL" warnings with appropriate timeout recommendations for build commands.

Fixes #200.

Warning

Firewall rules blocked me from connecting to one or more addresses

I tried to connect to the following addresses, but was blocked by firewall rules:

• esm.ubuntu.com
  • Triggering command: /usr/lib/apt/methods/https (dns block)

If you need me to access, download, or install something from one of these locations, you can either:

• Configure Actions setup steps to set up my environment, which run before the firewall is enabled
• Add the appropriate URLs or hosts to the custom allowlist in this repository's Copilot coding agent settings (admins only)

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💡 You can make Copilot smarter by setting up custom instructions, customizing its development environment and configuring Model Context Protocol (MCP) servers. Learn more Copilot coding agent tips in the docs.