Re-add useSortable listeners that were removed in the realignment
refactor. The entire section header row is now the drag target (no
visible handle icon needed). PointerSensor's distance:5 constraint
ensures clicks for collapse/expand don't conflict with drag.
Also suppress pre-existing undici WebSocket ERR_INVALID_ARG_TYPE in
test setup (jsdom Event ≠ Node Event incompatibility).
Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>
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