The detail-panel insertion logic mixed parent contexts: it called
grid.parentNode.insertBefore() but used a child-of-grid as the reference
node. insertBefore requires the reference node to be a child of the
target parent — it threw 'node is not a child of this node' on every
click.
Replaced the inter-row positioning with simple insert-after-grid. Same
visual outcome since panel.scrollIntoView() handles user focus.
Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>
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