refactor/add build time to page footers

src/hooks/useHtmlThemeAttr.jsx

@@ -0,0 +1,13 @@
+export function useHtmlThemeAttr () {
+  const [theme, setTheme] = useState(() =>
+    document.documentElement.getAttribute("data-theme") || "light"
+  );
+
+  useEffect(() => {
+    const handler = (e) => setTheme(e.detail);
+    document.addEventListener("set-theme", handler);
+    return () => document.removeEventListener("set-theme", handler);
+  }, []);
+
+  return theme;
+}