chore(code):Add cache room ID feature, no need to manually input room ID

frontend/lib/roomIdCache.ts

@@ -0,0 +1,37 @@
+// Utilities to cache a single room ID in browser localStorage
+// Works on client only; no-ops on server.
+
+const CACHED_KEY = "pd_cached_room_id_v1";
+
+function isClient() {
+  return typeof window !== "undefined";
+}
+
+export function getCachedId(): string | null {
+  if (!isClient()) return null;
+  try {
+    const v = window.localStorage.getItem(CACHED_KEY);
+    return v && v.trim() ? v : null;
+  } catch (_) {
+    return null;
+  }
+}
+
+export function setCachedId(id: string): void {
+  if (!isClient()) return;
+  try {
+    window.localStorage.setItem(CACHED_KEY, id);
+  } catch (_) {
+    // ignore
+  }
+}
+
+export function clearCachedId(): void {
+  if (!isClient()) return;
+  try {
+    window.localStorage.removeItem(CACHED_KEY);
+  } catch (_) {
+    // ignore
+  }
+}
+