refactor: Toast 升级为全局 Context，消除 onToast prop 透传

将 useToast 从独立 state hook 改为 Context-based，在 layout 中
挂载 ToastProvider 全局渲染 Toast。QrInviteModal、RoomManageModal、
ShareCardModal 不再需要 onToast prop，直接 useToast() 调用即可。
父组件 TopNav、MatchResult、profile、blindbox 移除了本地 Toast
渲染和 onToast 传递逻辑。

src/components/ShareCardModal.tsx

@@ -6,6 +6,7 @@ import { X, Download, Share2, Loader2, Star, MapPin, Zap } from "lucide-react";
 import { QRCodeSVG } from "qrcode.react";
 import { toPng } from "html-to-image";
 import type { Restaurant, MatchType, SceneType } from "@/types";
+import { useToast } from "@/hooks/useToast";
 
 type ShareCardData =
   | {
@@ -28,7 +29,6 @@ interface ShareCardModalProps {
   open: boolean;
   onClose: () => void;
   data: ShareCardData;
-  onToast?: (msg: string) => void;
 }
 
 async function loadImageAsDataUrl(src: string): Promise<string | null> {
@@ -775,8 +775,8 @@ export default function ShareCardModal({
   open,
   onClose,
   data,
-  onToast,
 }: ShareCardModalProps) {
+  const toast = useToast();
   const cardRef = useRef<HTMLDivElement>(null);
   const backdropRef = useRef<HTMLDivElement>(null);
   const [generating, setGenerating] = useState(false);
@@ -821,7 +821,7 @@ export default function ShareCardModal({
   const handleSave = useCallback(async () => {
     const png = await handleGenerate();
     if (!png) {
-      onToast?.("生成图片失败，请重试");
+      toast.show("生成图片失败，请重试");
       return;
     }
     const name =
@@ -829,13 +829,13 @@ export default function ShareCardModal({
         ? `NoWhatever_${data.restaurant.name}.png`
         : `NoWhatever_周末契约.png`;
     downloadDataUrl(png, name);
-    onToast?.("图片已保存");
-  }, [handleGenerate, onToast, data]);
+    toast.show("图片已保存");
+  }, [handleGenerate, toast, data]);
 
   const handleShare = useCallback(async () => {
     const png = await handleGenerate();
     if (!png) {
-      onToast?.("生成图片失败，请重试");
+      toast.show("生成图片失败，请重试");
       return;
     }
 
@@ -852,8 +852,8 @@ export default function ShareCardModal({
     }
 
     downloadDataUrl(png, "NoWhatever.png");
-    onToast?.("图片已保存，快去分享吧！");
-  }, [handleGenerate, onToast]);
+    toast.show("图片已保存，快去分享吧！");
+  }, [handleGenerate, toast]);
 
   const handleBackdropClick = (e: React.MouseEvent) => {
     if (e.target === backdropRef.current) onClose();