fix: AudioContext 复用 + 盲盒加载错误提示 + icon 按钮 aria-label

- #27: panic/blindbox/ShareCardModal/AuthModal 中 icon-only 按钮补 aria-label
- #28: playChime 缓存复用单个 AudioContext，避免超出浏览器 ~6 个上限
- #29: 已完成（上一批次 ApiError.name = "ApiError"）
- #30: blindbox lobby fetchRooms 失败时显示"加载失败/点击重试"
- #31: 已完成（theme.ts VALID_THEMES 校验）

src/app/blindbox/page.tsx

@@ -42,6 +42,7 @@ export default function BlindboxLobbyPage() {
   const [joinCode, setJoinCode] = useState("");
   const [joining, setJoining] = useState(false);
   const [error, setError] = useState("");
+  const [loadError, setLoadError] = useState(false);
 
   useEffect(() => {
     const registered = isRegistered();
@@ -65,12 +66,14 @@ export default function BlindboxLobbyPage() {
     const p = getCachedProfile();
     if (!p) return;
     setLoading(true);
+    setLoadError(false);
     try {
       const res = await fetch(`/api/blindbox/rooms?userId=${p.id}`);
+      if (!res.ok) throw new Error();
       const data = await res.json();
-      setRooms(data.rooms ?? []);
+      setRooms(Array.isArray(data.rooms) ? data.rooms : []);
     } catch {
-      /* ignore */
+      setLoadError(true);
     } finally {
       setLoading(false);
     }
@@ -219,6 +222,22 @@ export default function BlindboxLobbyPage() {
           </motion.div>
         ) : loading ? (
           <BlindboxListSkeleton />
+        ) : loadError ? (
+          <motion.div
+            key="load-error"
+            className="mt-16 flex flex-col items-center gap-3"
+            initial={{ opacity: 0, y: 20 }}
+            animate={{ opacity: 1, y: 0 }}
+          >
+            <Package size={36} className="text-purple-400/30" strokeWidth={1.5} />
+            <p className="text-sm text-muted">加载房间失败</p>
+            <button
+              onClick={fetchRooms}
+              className="mt-1 text-xs font-medium text-purple-400 active:text-purple-300"
+            >
+              点击重试
+            </button>
+          </motion.div>
         ) : rooms.length === 0 ? (
           /* ============ Layer 2: Logged in, no rooms — Create first ============ */
           <motion.div