refactor(eleventy): use dynamic path resolution for prismjs css

[jcbsfilho]

This pull request updates the Eleventy static site template to improve dependency handling and asset management, particularly for the Prism syntax highlighter CSS. It also makes minor housekeeping updates to version control files.

Asset management and dependency handling:

• Updated the passthrough copy in eleventy.config.js to dynamically resolve the path to prism-okaidia.css using Node's path module, ensuring compatibility regardless of where dependencies are installed. (eleventy.config.js) [1] [2]
• Updated all references to the Prism CSS file in Nunjucks templates to use the copied _site/css/prism-okaidia.css path instead of referencing node_modules directly. (_includes/layouts/base.njk, _includes/layouts/post.njk) [1] [2]

Version control and housekeeping:

• Added yarn.lock and pnpm-lock.yaml to .gitignore to prevent accidental commits of lockfiles from alternative package managers. (.gitignore)
• Removed the .nvmrc file, which previously specified Node.js version 16, to avoid enforcing a specific Node version. (.nvmrc)