Bug fixes and minor enhancements

Set height: 100% on crossfade panels wrapper

The dynamically created [data-tabs-panels] wrapper only had
position: relative, which gave it 0 height when panels use
height: 100% inside grid/flex layouts. Now the wrapper gets
height: 100% so the percentage chain resolves correctly and
panels fill the containing grid cell.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>