The skeletons right now are too jarring because they're visually heavier
than the content that comes in later. This makes them draw attention to
themselves as flashing things.

A good skeleton and loading indicator should ideally start as invisible
as possible and then gradually become more visible the longer time
passes so that if it loads quickly then it was never much visible at
all.

Even at its max it should never be heavier weight than the final content
so that it visually reverts into lesser. Another rule of thumb is that
it should be as close as possible to the final content in size but if
it's unknown it should always be smaller than the final content so that
the content grows into its slot rather than the slot contracting.

This makes the skeleton fade from invisible into the dimmest color just
as a subtle hint that something is still loading.

I also added a missing skeleton since the stack traces in rendered by
can now suspend while source mapping.

The other tweak I did is use disabled buttons in all the cases where we
load the ability to enable a button. This is more subtle and if you
hover over you can see why it's still disabled. Rather than flashing the
button each time you change element.