DankActions: conditional rendering based on exit code

Love DankActions! It's been a nice addition in an attempt to replace waybar, but one of the things I am struggling to do is have conditional elements in my dank bar. I think it could be nice to be able to conditionally show/hide actions depending on the exit code of a display command.

I had a quick look around to send a PR instead, but I'm struggling to fully remove the spacing of the hidden item so maybe someone with a better understanding of the layouting can do it more reasonable than me.

Start by locating the DankActions rendering and layout code for display commands in the Dank bar. Trace how an action's exit code could control visibility, then verify that hidden actions no longer leave unwanted spacing. Done means conditional show/hide behavior works without layout gaps.

Written by the indexing model from the issue text.