Remove index.md markdown to prevent 3.13 requirement

[jwilber]

The cards in the docs index.md require a specific format.
However, mdformat changes this format. To workaround this, we had to add excludes functionalty for mdformat that prevented it from formatting index.md. For some reason, the excludes functionality in mdformat which requires python 3.13. This is broke our nightly build.

To fix this, I've converted the index.md card logic from markdown to html, so that it no longer gets formatted. This removes the need for the excludes functionality and the 3.13 dependency it brings.

[copy-pr-bot]

This pull request requires additional validation before any workflows can run on NVIDIA's runners.

Pull request vetters can view their responsibilities here.

Contributors can view more details about this message here.

[jwilber]

/ok to test 641b1cb

[cspades]

Had to approve, the code was a bit hard to look at, approving minimizes those boxes. /s

(Also, how do you get that... byte code (?) from an SVG, can we always do this with any SVG we find?)

[pstjohn]

all relevant CI has passed, merging to save some time