Improve homepage Lighthouse performance

tools/build_site.py

@@ -37,6 +37,7 @@ BUILD_STEPS = [
     ("Inject SEO + rebuild sitemap/robots", ["tools/seo_inject.py", "--all", "--sitemap"]),
     ("Rebuild bot/AI discovery files", ["tools/build_botlinks.py"]),
     ("Rebuild offline assistant search index", ["tools/build_search_index.py"]),
+    ("Bundle and minify CSS", ["tools/build_css_bundle.py"]),
     # Last: stamp a content-hash ?v= on local CSS/JS refs so deploys aren't
     # served stale from cache. Must run after every step that writes pages.
     ("Cache-bust CSS/JS references", ["tools/cache_bust.py"]),