feat: add video conversion to HTML in Markdown parser

[saade]

This PR updates the markdown parsing to automatically turn specific URLs into <video> tags while ensuring there are no duplicates.

What’s New:

Convert URLs to <video>:

• Targets URLs like https://github.com/user-attachments/assets/....
• Replaces unique URLs with a <video> tag containing the proper attributes.
• Clean Up Duplicates:
  • If the same URL shows up multiple times, it only keeps the first conversion and removes the rest.

[danharrin]

Thanks!