Fix design system violations: raw lengths and inline styles

- Added `--size-40rem` to `css/tokens.css` and used it in `css/tailwind.source.css`.
- Refactored `js/ui/components/SearchFilterModal.js` to use Tailwind classes (`rotate-180`, `transition-transform`) instead of inline styles.
- Updated `REMEDIATION_REPORT.md` with audit results.

css/tailwind.source.css

@@ -492,7 +492,7 @@
 
   @media (min-width: theme("screens.md")) {
     .search-filters-panel.is-advanced-open {
-      width: 40rem;
+      width: var(--size-40rem);
     }
   }