feat(frontend): implement pool views and add-to-pool from file list

- Add /pools list page with search, sort, load-more pagination
- Add /pools/new create form (name, notes, public toggle)
- Add /pools/[id] detail page: metadata editing, ordered file grid,
  drag-to-reorder, filter bar, file selection/removal, add-files overlay
- Add pool sort store (poolSorting) to sorting.ts
- Wire "Add to pool" button in SelectionBar: bottom-sheet pool picker
  loads pool list, user picks one, selected files are POSTed to pool
- Add full pool mock API handlers in vite-mock-plugin.ts (CRUD + file
  management: add, remove, reorder with cursor pagination)

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

frontend/src/lib/stores/sorting.ts

@@ -48,4 +48,11 @@ export type CategorySortField = 'name' | 'color' | 'created';
 export const categorySorting = makeSortStore<CategorySortField>('sort:categories', {
 	sort: 'name',
 	order: 'asc',
+});
+
+export type PoolSortField = 'name' | 'created';
+
+export const poolSorting = makeSortStore<PoolSortField>('sort:pools', {
+	sort: 'created',
+	order: 'desc',
 });