feat(ui): shared card grid with max six columns and virtualization

Add cardGridLayout helpers, useCardGridMetrics, useRemeasureGridVirtualizer, and VirtualCardGrid (TanStack row virtualization, always remeasure on layout changes).

Apply to Artists (grid + list unchanged policy), Albums, Composers grid, playlists, radio stations, offline library, and album-heavy browse/detail pages. Respect disableMainstageVirtualLists for a non-virtual grid with the same column rules.

Includes vitest coverage for column cap.

src/hooks/useRemeasureGridVirtualizer.ts

@@ -0,0 +1,24 @@
+import { useEffect } from 'react';
+import type { Virtualizer } from '@tanstack/react-virtual';
+
+/** When grid column count or row height estimate changes, TanStack can keep stale offsets until scroll — force a remeasure. */
+export function useRemeasureGridVirtualizer<TScroll extends Element, TItem extends Element>(
+  virtualizer: Virtualizer<TScroll, TItem>,
+  args: {
+    active: boolean;
+    gridCols: number;
+    rowHeightEst: number;
+    virtualRowCount: number;
+  },
+): void {
+  useEffect(() => {
+    if (!args.active || args.virtualRowCount === 0) return;
+    virtualizer.measure();
+  }, [
+    args.active,
+    args.gridCols,
+    args.rowHeightEst,
+    args.virtualRowCount,
+    virtualizer,
+  ]);
+}