fix: 房间不存在时展示错误页面，替代无限加载转圈

src/app/room/[id]/page.tsx

@@ -1,7 +1,7 @@
 "use client";
 
 import { useEffect, useState, useCallback } from "react";
-import { useParams } from "next/navigation";
+import { useParams, useRouter } from "next/navigation";
 import TopNav from "@/components/TopNav";
 import SwipeDeck from "@/components/SwipeDeck";
 import { useRoomPolling } from "@/hooks/useRoomPolling";
@@ -9,13 +9,15 @@ import { getUserId } from "@/lib/userId";
 
 export default function RoomPage() {
   const params = useParams<{ id: string }>();
+  const router = useRouter();
   const roomId = params.id;
 
   const [userId, setUserId] = useState("");
   const [joined, setJoined] = useState(false);
+  const [joinFailed, setJoinFailed] = useState(false);
 
   const {
-    userCount, match, matchType, matchLikes, runnerUps, likeCounts, swipeCounts, restaurants, mutate,
+    userCount, match, matchType, matchLikes, runnerUps, likeCounts, swipeCounts, restaurants, notFound, mutate,
   } = useRoomPolling(roomId);
 
   useEffect(() => {
@@ -26,7 +28,10 @@ export default function RoomPage() {
       method: "POST",
       headers: { "Content-Type": "application/json" },
       body: JSON.stringify({ userId: id }),
-    }).then(() => setJoined(true));
+    }).then((res) => {
+      if (res.ok) setJoined(true);
+      else setJoinFailed(true);
+    }).catch(() => setJoinFailed(true));
   }, [roomId]);
 
   const handleReset = useCallback(async () => {
@@ -43,6 +48,22 @@ export default function RoomPage() {
     await mutate();
   }, [roomId, mutate]);
 
+  if (notFound || joinFailed) {
+    return (
+      <div className="flex h-dvh flex-col items-center justify-center gap-4 bg-background px-6">
+        <p className="text-4xl">🍜</p>
+        <p className="text-base font-semibold text-zinc-700">房间不存在或已过期</p>
+        <p className="text-sm text-zinc-400">房间号可能有误，或房间已超过 24 小时</p>
+        <button
+          onClick={() => router.push("/")}
+          className="mt-2 h-10 rounded-xl bg-emerald-500 px-6 text-sm font-bold text-white shadow-sm transition-colors hover:bg-emerald-600"
+        >
+          返回首页
+        </button>
+      </div>
+    );
+  }
+
   const initialIndex = swipeCounts[userId] ?? 0;
   const ready = joined && userId && restaurants.length > 0;