feat(core): apply glass effect to sticky DataTable header

[JianJroh]

Description

The sticky DataTable header used a transparent background, so the scrolled body rows visibly bled through it. Switching to a glass-style header — semi-transparent tint + backdrop blur — hides the rows behind it and matches the panel's bg-glass aesthetic.

Reproducible in the Recent Commits table of the plugin-git-ui example.

Before	After
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Additional context

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commit: 565e3be