Added LLM-digestible documentation and sample .cursorrules file

[chriscarrollsmith]

• Added cursorrules.txt file as a downloadable static asset
• Added a code block in index.qmd that generates an llms.txt file with the full project documentation
  • Gets all documentation file paths from _quarto.yml
  • Gets the text content of all the documentation files and replaces the Quarto header with a normal Markdown title
  • Concatenates the file contents and writes them to a single llms.txt file
• Added download links for these files to the project docs