Mark prose only while somebody is pointing at the card

Standing marks are out. A plan accumulates decisions, so anything painted
permanently ends up painted over most of the document, and a page that is
mostly highlighted has told the reader nothing. Which prose a comment or a
decision concerns is the sidecar's question to answer, and it answers on
demand.

That leaves one highlight rather than three, so the tone vocabulary goes with
them: no comment amber, no decision wash, no priority ordering between marks
that can no longer overlap. Both halves of the sidecar declare the same thing
and the union is painted, which is what the per-owner registry was for.

Where a thread points is still worked out for every thread, focused or not:
that is what says whether it has drifted and where it sorts in the pane. Only
the drawing is conditional.

Removed the hit-testing that would have let a click on marked prose focus its
card. It was written against a standing mark, nothing ever called it, and with
nothing painted at rest there is no longer anything to click.