Jimena/docs updates part 2

[jdupre81]

Content Updates and Design Adjustments

This Pull Request includes several content enhancements and design modifications across the site:

• Landing Page Design Tweaks: Various aesthetic adjustments have been implemented on the main page.
  • ⚠️ Dark Mode Issue (Requires UI Team Review): The Dark Mode styling is not rendering correctly only on the Landing Page (the rest of the site works as expected).
• Content and Link Cleanup: Content across several pages has been reviewed and updated. Specifically, numerous links previously redirecting to Notion pages have been migrated to point to internal documentation.
• Visuals: The documentation has been enriched with the addition of images and videos.

File Structure Request

Please Note: I am unable to resolve the path error for the following file, which needs to be moved for logical organization:

• Action Required: Could you please move the file "How the CSCS integration works in Renkulab" (40-css-integration.md) from its current location to the target path: 60-sessions/guides/ (under the "Compute Sessions/How to..." section). Thanks in advance

[rokroskar]

Live build of this PR on readthedocs.