- Updated project to Astro 5.2 for improved performance and new featu…

…res.

- Replaced static last modified time with dynamic Git commit timestamp to reflect the actual last modification date of content.
- Optimized RSS feed generation by:
  - Adding Markdown-It to convert markdown content to HTML.
  - Using sanitize-html to ensure content is sanitized, allowing only necessary HTML tags (e.g., img, h1, h2).
  - Enhanced RSS item structure for cleaner and more efficient output.
  - Updated feed metadata and improved feed formatting for better compatibility and SEO.