HCP/PAT.DEV: Improve "Go back to last slide" button on all-done-slide

Do not implement: close when https://gitlab.com/recoverycat/rcc-client/-/issues/749 is done

Go back to last slide button on the all-done-slide is sticky and feels not well thought through.

Don't necessarily have a better solution for this. Maybe making it 50% transparent on the last slide, but on hover back to 100% visibility. Not sure, if this is the best approach for mobile though.