Fix/doc links

[Romulad]

What:

• Fixed .md links in the docs/ folder by appending the .md extension to avoid 404 errors when browsing on GitHub.
• Added a custom rehype plugin to the Astro site under website/ to remove .md extensions from built links on the live documentation site, keeping the URLs clean while preserving functionality.

Why:

• Similar to what was reported in PR docs: fix docs link, improve liking #32: navigating through the GitHub docs leads to broken links (e.g., introduction.md pointing to other docs without .md and returning 404s).
• To prevent the website build from breaking, the rehype plugin strips .md only during the static site generation, so both GitHub and the live site remain functional and consistent.

How:

• Manually updated internal links in Markdown files within the docs/ directory.
• Created a simple rehype plugin in website/ that removes the .md extension from links during the Astro build phase, while keeping original links in the source untouched.

Checklist:

• Tests " N/A"
• TypeScript definitions updated "N/A"
• Ready to be merged
  

Note:
I discovered this project while working on a CLI app and also came across your work—which I truly admire. I'm currently reading your book The Framework Field Guide – Fundamentals (on Chapter 5!), and I'm really excited about what's coming next with the Ecosystem and Internals. Thanks for all the value you're putting into the community.