[FIX]: Table header background is transparent so rows show through on scroll

[marwan562]

The sticky table header has no solid background, so when you scroll the table vertically the row data shows through behind the column names (id, category_id, name, sku, price, stock, is_published, metadata all overlap).

Steps to reproduce:

1. Open any table with enough rows to scroll (e.g. products).
2. Scroll down.
3. The header row stays sticky but body text is visible behind it.

Expected: the header keeps a solid background in both dark and light mode so rows slide underneath it without showing through.

Root cause: the header row uses a translucent bg-muted/40 class and the parent thead has no background at all (packages/web/src/features/tables/components/table-head.tsx:20, table-head-row.tsx:142). Same pattern exists in the shared data grid (packages/ui/src/data-display/data-grid/data-grid-head.tsx), the query runner result header (packages/web/src/features/query-runner/components/table-view.tsx:52), and the referenced-table header (packages/web/src/features/records/components/referenced-table.tsx:142).

Suggested fix: give the sticky header an opaque theme-aware background (bg-muted) on both thead and the header row so it works in dark and light mode.

Screenshot