fix: 移除静默 fallback 数据，API 失败时明确提示用户

src/app/page.tsx

@@ -153,20 +153,21 @@ export default function LandingPage() {
         body: JSON.stringify({ ...coords, radius, priceRange, cuisine, userId: getUserId() }),
       });
 
+      const data = await res.json();
+
       if (!res.ok) {
-        throw new Error("创建房间失败");
+        throw new Error(data.error || "创建房间失败");
       }
 
-      const { roomId } = await res.json();
-      if (!roomId) {
+      if (!data.roomId) {
         throw new Error("创建房间失败");
       }
 
       setLoadingText("正在进入房间...");
-      await joinRoom(roomId);
-      router.push(`/room/${roomId}`);
-    } catch {
-      setError("创建失败，请重试");
+      await joinRoom(data.roomId);
+      router.push(`/room/${data.roomId}`);
+    } catch (e) {
+      setError(e instanceof Error ? e.message : "创建失败，请重试");
       setLoading(false);
       setLoadingText("");
     }