refactor(helpers): modernize reactive helpers and add tests

src/shared/lib/helpers/index.ts

@@ -1,3 +1,27 @@
+/**
+ * Reactive helper factories using Svelte 5 runes
+ *
+ * Provides composable state management patterns for common UI needs:
+ * - Filter management with multi-selection
+ * - Typography controls with bounds and stepping
+ * - Virtual scrolling for large lists
+ * - Debounced state for search inputs
+ * - Entity stores with O(1) lookups
+ * - Character-by-character font comparison
+ * - Persistent localStorage-backed state
+ * - Responsive breakpoint tracking
+ * - 3D perspective animations
+ *
+ * @example
+ * ```ts
+ * import { createFilter, createVirtualizer, createTypographyControl } from '$shared/lib/helpers';
+ *
+ * const filter = createFilter({ properties: [...] });
+ * const virtualizer = createVirtualizer(() => ({ count: 1000, estimateSize: () => 50 }));
+ * const control = createTypographyControl({ value: 16, min: 12, max: 72, step: 1 });
+ * ```
+ */
+
 export {
     createFilter,
     type Filter,