refactor: 提取 useShare hook，统一分享和剪贴板逻辑

新增 useShare（Web Share API + clipboard fallback），
消除 QrInviteModal、BlindboxRoomPage、ShareCardModal 三处重复的分享代码。

src/app/blindbox/[code]/page.tsx

@@ -25,6 +25,7 @@ import { getCachedProfile, isRegistered } from "@/lib/userId";
 import ShareCardModal from "@/components/ShareCardModal";
 import Button from "@/components/Button";
 import { useToast } from "@/hooks/useToast";
+import { useShare } from "@/hooks/useShare";
 import { BlindboxRoomSkeleton } from "@/components/Skeleton";
 import type { UserProfile } from "@/types";
 
@@ -391,32 +392,21 @@ export default function BlindboxRoomPage() {
     setTimeout(frame, 200);
   };
 
-  const handleCopyCode = async () => {
-    if (!room) return;
-    try {
-      await navigator.clipboard.writeText(room.code);
-      toast.show("房间号已复制");
-    } catch { /* ignore */ }
-  };
+  const { share, copyToClipboard } = useShare();
 
-  const handleShare = async () => {
+  const handleCopyCode = useCallback(
+    () => room ? copyToClipboard(room.code, "房间号已复制") : undefined,
+    [room, copyToClipboard],
+  );
+
+  const handleShare = useCallback(() => {
     if (!room) return;
     const url = typeof window !== "undefined" ? `${window.location.origin}/blindbox/${room.code}` : "";
-    const shareData = {
-      title: `周末契约 · ${room.name}`,
-      text: `来和我一起玩周末盲盒吧！房间号：${room.code}`,
-      url,
-    };
-    try {
-      if (navigator.share && navigator.canShare?.(shareData)) {
-        await navigator.share(shareData);
-        return;
-      }
-    } catch (e) {
-      if (e instanceof Error && e.name === "AbortError") return;
-    }
-    handleCopyCode();
-  };
+    share(
+      { title: `周末契约 · ${room.name}`, text: `来和我一起玩周末盲盒吧！房间号：${room.code}`, url },
+      handleCopyCode,
+    );
+  }, [room, share, handleCopyCode]);
 
   const isCreator = profile?.id === room?.creatorId;