feat(admin): async bulk delete with toasts

README.md

@@ -115,6 +115,7 @@ npm run build
    - Long titles/URLs are truncated; hover to see the full value. Click to copy.
    - Drag the column separators to resize; click headers to sort (double-click a separator to reset width).
 4. Use **Select Results** to select the filtered rows, then click **Delete Selected**.
+   - Bulk deletes run in small batches so the UI stays responsive. Keep the tab open until it finishes.
 5. For legitimate feeds that got spam emails, open **Emails**, filter by subject, then **Select Results** and **Delete Selected**.
 
 ## Upgrading dependencies