draw selection over top; connected to selected captures display issues

[disconcision]

sometimes selections are cut off a bit. other times (selected captures) they are barely visible. drawing over top would fix the first case, but might screw up the second if not special-cased? unless we draw just the outline over top: this is sufficient for the first, and probably adequate for the second.

so:

1. fish selection out stx
2. figure out how we're drawing selection outlines
3. copy that code to top-level layout, and make a new popout-layer

[disconcision]

upgraded to garbage fire due to poor visibility issues for selector on captures

[disconcision]

selection now drawn over top... capture issue still needs work