Show resolved decisions as margin markers beside their prose

A linked, answered decision collapses out of the plan and becomes a gutter
marker on the first line of the first anchored block. Hovering the marker or
the prose washes the passage and previews the decision; pressing pins the
popover, which also lists the options not chosen. Pending, empty and orphaned
decisions keep a compact card. The decisions pane is unchanged.

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