refactor(lib): relocate cardGridLayout → lib/util (store-free)

cardGridLayout's only store dep was three grid-column constants it imported from
authStoreDefaults. Flipped ownership: the constants now live in lib/util/cardGridLayout
(pure layout config) and authStoreDefaults re-exports them (store→lib), so the auth
settings clamp/default and every existing consumer are unchanged. cardGridLayout is now
store-free and homes in lib/util alongside the other pure helpers — consumed cleanly by
ui/VirtualCardGrid + cover/layoutSizes. Resolves the documented store-free-lib block for
the card-grid layout helper. Pure move + constant relocation; tests pass unmodified.

src/cover/layoutSizes.ts

@@ -1,4 +1,4 @@
-import { computeCardGridColumnCount, computeCellWidthPx } from '../utils/cardGridLayout';
+import { computeCardGridColumnCount, computeCellWidthPx } from '@/lib/util/cardGridLayout';
 
 export const COVER_DENSE_SEARCH_CSS_PX = 40;
 /** Artist detail top-track thumb (32×32 CSS px). */

src/features/album/pages/Albums.tsx

@@ -7,7 +7,7 @@ import { albumGridWarmCovers, coverDisplayCssPxForAlbumGrid } from '@/cover/layo
 import { useLibraryCoverPrefetch } from '@/cover/useLibraryCoverPrefetch';
 import { useAuthStore } from '@/store/authStore';
 import { clampLibraryGridMaxColumns } from '@/store/authStoreHelpers';
-import { computeCardGridColumnCount } from '@/utils/cardGridLayout';
+import { computeCardGridColumnCount } from '@/lib/util/cardGridLayout';
 import GenreFilterBar from '@/ui/GenreFilterBar';
 import YearFilterButton from '@/ui/YearFilterButton';
 import StarFilterButton from '@/ui/StarFilterButton';

src/hooks/useCardGridMetrics.ts

@@ -6,7 +6,7 @@ import {
   computeCardGridColumnCount,
   computeCellWidthPx,
   estimateRowHeightPx,
-} from '../utils/cardGridLayout';
+} from '@/lib/util/cardGridLayout';
 
 /**
  * ResizeObserver-driven column count (capped by Settings → Library) and

src/lib/util/cardGridLayout.test.ts

@@ -1,6 +1,6 @@
 import { describe, expect, it } from 'vitest';
-import { computeCardGridColumnCount, estimateRowHeightPx } from './cardGridLayout';
-import { LIBRARY_GRID_MAX_COLUMNS_MAX, LIBRARY_GRID_MAX_COLUMNS_MIN } from '../store/authStoreDefaults';
+import { computeCardGridColumnCount, estimateRowHeightPx } from '@/lib/util/cardGridLayout';
+import { LIBRARY_GRID_MAX_COLUMNS_MAX, LIBRARY_GRID_MAX_COLUMNS_MIN } from '@/store/authStoreDefaults';
 
 describe('estimateRowHeightPx', () => {
   describe('composer variant', () => {

src/lib/util/cardGridLayout.ts

@@ -3,16 +3,17 @@
  * and row-height estimates derived from measured cell width (TanStack virtual rows).
  */
 
-import {
-  DEFAULT_LIBRARY_GRID_MAX_COLUMNS,
-  LIBRARY_GRID_MAX_COLUMNS_MAX,
-  LIBRARY_GRID_MAX_COLUMNS_MIN,
-} from '../store/authStoreDefaults';
+// Library grid column config. Owned here (pure layout math) and re-exported by
+// authStoreDefaults, which clamps/defaults the user's libraryGridMaxColumns
+// setting against them — keeps this module store-free so ui/ + cover/ can use it.
+export const DEFAULT_LIBRARY_GRID_MAX_COLUMNS = 6;
+export const LIBRARY_GRID_MAX_COLUMNS_MIN = 4;
+export const LIBRARY_GRID_MAX_COLUMNS_MAX = 12;
 
 export const CARD_GRID_GAP_PX = 16;
 export const CARD_GRID_MIN_TILE_PX = 140;
 
-/** @deprecated use `DEFAULT_LIBRARY_GRID_MAX_COLUMNS` from `authStoreDefaults` */
+/** @deprecated use `DEFAULT_LIBRARY_GRID_MAX_COLUMNS` */
 export const CARD_GRID_MAX_COLS = DEFAULT_LIBRARY_GRID_MAX_COLUMNS;
 
 export function computeCardGridColumnCount(containerWidthPx: number, maxColumns: number): number {

src/store/authStoreDefaults.ts

@@ -42,7 +42,13 @@ export const MIX_MIN_RATING_FILTER_MAX_STARS = 3;
 
 export const RANDOM_MIX_SIZE_OPTIONS: readonly number[] = [50, 75, 100, 125, 150];
 
-/** Default max columns for album/artist/playlist card grids (Settings → Library). */
-export const DEFAULT_LIBRARY_GRID_MAX_COLUMNS = 6;
-export const LIBRARY_GRID_MAX_COLUMNS_MIN = 4;
-export const LIBRARY_GRID_MAX_COLUMNS_MAX = 12;
+/**
+ * Default + clamp bounds for album/artist/playlist card grids (Settings → Library).
+ * Defined in lib/util/cardGridLayout (store-free layout math) and re-exported here
+ * so the auth-store settings clamp/default and all existing consumers are unchanged.
+ */
+export {
+  DEFAULT_LIBRARY_GRID_MAX_COLUMNS,
+  LIBRARY_GRID_MAX_COLUMNS_MIN,
+  LIBRARY_GRID_MAX_COLUMNS_MAX,
+} from '@/lib/util/cardGridLayout';

src/ui/VirtualCardGrid.tsx

@@ -7,7 +7,7 @@ import { useElementClientHeightById } from '@/lib/hooks/useResizeClientHeight';
 import { useCardGridMetrics } from '@/hooks/useCardGridMetrics';
 import { useRemeasureGridVirtualizer } from '@/lib/hooks/useRemeasureGridVirtualizer';
 import { useVirtualizerScrollMargin } from '@/lib/hooks/useVirtualizerScrollMargin';
-import type { CardGridRowHeightVariant } from '@/utils/cardGridLayout';
+import type { CardGridRowHeightVariant } from '@/lib/util/cardGridLayout';
 
 export type VirtualCardGridProps<T> = {
   items: readonly T[];