Fix Studio card markup and improve furni browsing UX

- Fix invalid nested button elements in furni grid cards that broke
  card borders, hover styles and selection rendering
- Fix stale-closure bug where switching furni source fetched from the
  previously selected source
- Add progress bar plus Cancel/Dismiss controls to batch imports
- Make the detail drawer an overlay on small screens
- Add clear-search and clear-selection actions in the toolbar
- Use pixelated image rendering and keyboard focus rings on cards

src/components/admin/studio/catalog-rail.tsx

@@ -67,7 +67,7 @@ export function CatalogRail({
 									onSelect(selectedId === node.id ? null : node.id);
 								}}
 								className={cn(
-									"group flex w-full items-center gap-1.5 rounded-md px-1.5 py-1.5 text-left text-xs transition-colors",
+									"group flex w-full cursor-pointer items-center gap-1.5 rounded-md px-1.5 py-1.5 text-left text-xs transition-colors outline-none focus-visible:ring-2 focus-visible:ring-[var(--admin-accent)]",
 									selectedId === node.id
 										? "bg-[var(--admin-accent)]/15 text-[var(--admin-text)]"
 										: "text-[var(--admin-text-muted)] hover:bg-[var(--admin-accent)]/10 hover:text-[var(--admin-text)]",