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/[code]/page.tsx

@@ -334,6 +334,7 @@ export default function BlindboxRoomPage() {
       <div className="flex w-full max-w-sm items-center gap-3">
         <button
           onClick={() => router.push("/blindbox")}
+          aria-label="返回"
           className="flex h-8 w-8 shrink-0 items-center justify-center rounded-full bg-surface ring-1 ring-border transition-colors active:bg-elevated"
         >
           <ArrowLeft size={16} className="text-muted" />
@@ -363,6 +364,7 @@ export default function BlindboxRoomPage() {
 
         <button
           onClick={() => setShowInvite(!showInvite)}
+          aria-label="邀请成员"
           className="flex h-8 w-8 shrink-0 items-center justify-center rounded-full bg-purple-600/15 text-purple-400 ring-1 ring-purple-500/20 transition-colors active:bg-purple-600/25"
         >
           <Share2 size={14} />
@@ -486,6 +488,7 @@ export default function BlindboxRoomPage() {
                   <button
                     onClick={handleSubmit}
                     disabled={!input.trim() || submitting}
+                    aria-label="提交想法"
                     className="flex h-12 w-12 items-center justify-center rounded-xl bg-purple-600 text-white transition-colors hover:bg-purple-500 disabled:opacity-30"
                   >
                     {submitting ? <Loader2 size={18} className="animate-spin" /> : <Send size={18} />}

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

src/app/panic/page.tsx

@@ -297,6 +297,7 @@ export default function PanicPage() {
             {(selectedLocation || locationQuery) && !loading && (
               <button
                 onClick={clearLocation}
+                aria-label="清除位置"
                 className="absolute right-2.5 flex h-5 w-5 items-center justify-center rounded-full text-muted hover:text-secondary"
               >
                 <X size={14} />
@@ -399,6 +400,7 @@ export default function PanicPage() {
               {cuisine && !loading && (
                 <button
                   onClick={() => setCuisine("")}
+                  aria-label="清除口味"
                   className="absolute right-2 flex h-4 w-4 items-center justify-center rounded-full text-muted hover:text-secondary"
                 >
                   <X size={12} />
@@ -515,6 +517,7 @@ export default function PanicPage() {
           <button
             type="submit"
             disabled={loading || roomCode.length !== 4}
+            aria-label="加入房间"
             className="flex h-11 w-11 items-center justify-center rounded-xl bg-elevated text-secondary ring-1 ring-subtle transition-colors hover:bg-subtle disabled:opacity-30"
           >
             <LogIn size={18} />