chore: complete clean Agent Desk source snapshot

web/hooks/use-lg-media.ts

@@ -0,0 +1,25 @@
+"use client";
+
+import { useSyncExternalStore } from "react";
+
+/** Matches Tailwind's default `lg` breakpoint (1024px). */
+const LG_MEDIA_QUERY = "(min-width: 1024px)";
+
+function subscribe(onStoreChange: () => void) {
+  const mq = window.matchMedia(LG_MEDIA_QUERY);
+  mq.addEventListener("change", onStoreChange);
+  return () => mq.removeEventListener("change", onStoreChange);
+}
+
+function getSnapshot() {
+  return window.matchMedia(LG_MEDIA_QUERY).matches;
+}
+
+function getServerSnapshot() {
+  return false;
+}
+
+/** Client-only true at lg and above. SSR always returns false for mobile-first rendering. */
+export function useIsLgUp() {
+  return useSyncExternalStore(subscribe, getSnapshot, getServerSnapshot);
+}