Rows at warning severity or above already sort first. They now sit under
a small "Needs you" label with a hairline before the rest, and there
are no headers at all when nothing is waiting. The pure section_header
rule is unit-tested. The row close button scales on press like the pane
actions.

Co-Authored-By: Claude Opus 5.5 (1M context) <noreply@anthropic.com>