docs(ai): improve onboarding steps and fix lint

- Fix `npm run lint` failure by replacing inline style with CSS class in `js/ui/components/SearchFilterModal.js`.
- Fix `npm run lint:tokens` failure by defining `--size-40rem` in `css/tokens.css` and using it in `css/tailwind.source.css`.
- Update `CONTRIBUTING.md` with troubleshooting tips for unit test hangs and linting failures.
- Attempt to update `caniuse-lite` to silence build warning (may persist due to environment/cache).

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);
     }
   }