The layout-tree renderer (63a9bde77) introduced PaneTabLabel with a
text-[9px] override that contradicts the parent PaneTab's baseline of
text-[0.6875rem] (11px). The old ChatHeader/TitleMenuTrigger used 0.75rem
(12px), making 9px a clear regression.
Drop the explicit size class from the label span so it inherits 0.6875rem
from the parent — consistent typographic hierarchy, still a meaningful
improvement over 9px.
d939624916