Updating GitHub Copilot WTH

[Whowong]

This pull request introduces a new What The Hack (WTH) content authoring assistant chat mode and updates the GitHub Copilot hack's coach guide and solutions to reflect best practices, expanded challenge structure, and improved instructional clarity. The changes enhance guidance for both authors and coaches, ensure compliance with WTH standards, and improve the educational value of the hackathon experience.

WTH Content Authoring Assistant

New authoring assistant and guidelines:

• Added .github/chatmodes/WTHAuthor.chatmode.md to provide a comprehensive assistant for creating WTH-compliant content, including detailed instructions, required structure, templates, and review checklists for hackathons.

GitHub Copilot Hack Structure & Content

Expanded challenge structure:

• Updated 071-GitHubCopilot/Coach/README.md to add new challenges focused on Model Context Protocol (MCP), custom agents, and chat modes; increased the total number of challenges from five to six with revised titles and descriptions.
• Adjusted time estimates for each challenge to accommodate the expanded structure and provide clearer guidance for event pacing.

Enhanced instructional guidance:

• Improved explanations in Coach/Solution-01.md to clarify different interaction methods with GitHub Copilot, including inline completions, chat panel, context menu, and more, ensuring students and coaches are aware of all available features.
• Significantly expanded best practices and prompt engineering guidance in Coach/Solution-02.md, including step-by-step demonstration recommendations, techniques to avoid ambiguity, context management, and coding practices for optimal Copilot use.