refactor(shared): keep BaseQueryStore out of the lib barrels

BaseQueryStore pulls @tanstack/query-core. Re-exporting it through the
broad $shared/lib and $shared/lib/helpers barrels made every consumer of
those barrels eager-load TanStack at module-eval time (no tree-shaking in
vitest/vite-node), which is what surfaced the queryClient mock init-order
failure. Its single consumer now imports it by path.

src/shared/lib/helpers/index.ts

@@ -137,7 +137,8 @@ export {
     type PerspectiveManager,
 } from './createPerspectiveManager/createPerspectiveManager.svelte';
 
-/**
- * Base Query store using Tanstack query
+/*
+ * BaseQueryStore is intentionally NOT re-exported here.
+ * It pulls @tanstack/query-core, so routing it through this leaf barrel would
+ * make every consumer of the barrel eager-load TanStack. Import it by path.
  */
-export { BaseQueryStore } from './BaseQueryStore/BaseQueryStore.svelte';