Make the decision marker, not the prose, open resolved decisions

Hovering prose behind a resolved decision no longer washes it or previews
the decision. Only the margin marker does: hover or keyboard focus previews
and washes, a press pins the popover. The marker answers within 12px of its
edge, clipped so the reach never covers the prose. The marker icon is now
the settled green instead of the generic icon grey.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>