feat: upgrade from Tailwind v3 to v4

See Tailwind v4 breaking changes: https://tailwindcss.com/docs/upgrade-guide
See Hugo's new integration with Tailwind v4: https://gohugo.io/functions/css/tailwindcss/

Close #3211

.github/workflows/build-test-site.yaml

@@ -34,8 +34,11 @@ jobs:
             - recursive: false
               args: [--frozen-lockfile]
 
-#      - name: Install JS dependencies
-#        run: rm -rf node_modules && pnpm install --frozen-lockfile
+      - name: Install Tailwind v4 dependencies
+        run: |
+          cd modules/blox-tailwind
+          pnpm install --frozen-lockfile
+          cd ../..
 
       - name: Check for linting errors
         run: pnpm run lint:js  # TODO: also lint styles again once new rule errors resolved