fix: css pipeline & styling

[j-mes]

This pull request refactors the CSS setup and organization, improves the build pipeline, and cleans up markup for better maintainability and clarity. The main changes include splitting base styles into a dedicated file, updating CSS imports to use layers, making the CSS build process environment-aware, and simplifying the post layout. Additionally, minor improvements were made to the CSS reset for consistency.

CSS organization and build pipeline improvements:

• Moved base styles from index.css into a new base.css file, improving separation of concerns and maintainability. (src/styles/base.css)
• Updated index.css to use CSS @import with layers for reset.css and base.css, replacing the previous inline layering and imports. (src/styles/index.css)

Build process enhancements:

• Refactored the PostCSS pipeline in setup-css.js to only run the CSS minifier (postCssCsso) in production, improving build performance during development. (src/helpers/setup-css.js)
• Added more granular watch targets for CSS files in src/styles and src/components to ensure changes are picked up during development. (src/helpers/setup-css.js)

Markup and style cleanup:

• Simplified the post.njk layout by removing the header section, focusing the template on content and navigation. (src/layouts/post.njk)
• Minor consistency improvements to attribute quoting and formatting in reset.css. (src/styles/reset.css) [1] [2] [3] [4] [5]