feat(admin): resizable + sortable table columns

AGENTS.md

@@ -79,6 +79,7 @@ Notes:
 
 - First choice: use dashboard bulk actions (`/admin`) with search + checkbox selection.
 - Use **Table** view for bulk delete.
+- Table columns are resizable and sortable; widths persist per-browser via localStorage.
 - Avoid wildcard deletion; prefer search + small batches to reduce risk of deleting legitimate feeds.
 
 ## Cloudflare/Wrangler conventions