fix: Integrate preprocessed images into markdown

Currently, `vite.config.mjs` runs the `image-preprocess.mjs` and preprocesses the image. However, these images are not used in rendering of the markdown. Performance is left on the table, and preprocessing currently is just overhead.

_Notes of the maintainer_
I've tried unsuccessfully to change the image path in the .md during the build process, but I feel like you should be able to first pick the right image, so that _might_ mean passing args to the build script from vite, and _maybe_ serve different images based on width (using css maybe? idk, but this implementation will be bonus :) ). Otherwise, just pick one res, edit the preprocess script accordingly and integrate the preprocess images. :)

I'm pretty sure there's an easier way, but i've been dense so far