Restore AI instructions in README.md wrapped in XML comments

[Copilot]

This PR restores the AI instructions section that was removed in commit 17aac7a, but wraps it in XML comments to keep it hidden from regular README viewers while maintaining accessibility in the source code.

Changes

The restored content includes:

• For AI Agents: Instructions pointing to the comprehensive GitHub Agentic Workflows documentation at .github/instructions/github-agentic-workflows.instructions.md
• Prompt Template: Reference to the /create-agentic-workflow prompt template for GitHub Copilot Chat

Rationale

By wrapping this content in XML comments (<!-- -->), we achieve:

1. Clean README rendering: The instructions don't appear when viewing the README on GitHub or in documentation
2. Source code preservation: The information remains available in the raw markdown for AI agents and developers who need it
3. Discoverability: AI agents that can read HTML comments in markdown files can still access these instructions

Testing

• ✅ Build succeeds with no errors
• ✅ All unit tests pass
• ✅ No functional changes to the codebase

Original prompt

Restore AI instructions removed in this commit but wrap them in an XML comment.

17aac7a

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✨ Let Copilot coding agent set things up for you — coding agent works faster and does higher quality work when set up for your repo.

[github-actions]

Agentic Changeset Generator triggered by this pull request.