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).

js/ui/components/SearchFilterModal.js

@@ -168,10 +168,10 @@ function toggleAdvanced(forceState = null) {
 
   if (newState) {
     advancedPanel.classList.remove("hidden");
-    advancedChevron.style.transform = "rotate(180deg)";
+    advancedChevron.classList.add("rotate-180");
   } else {
     advancedPanel.classList.add("hidden");
-    advancedChevron.style.transform = "rotate(0deg)";
+    advancedChevron.classList.remove("rotate-180");
   }
 }