refactor: 提取 useToast hook + Toast 组件，消除 4 处重复的通知逻辑

将 state + setTimeout 自动消失逻辑封装为 useToast hook，
Toast UI 统一为组件支持 top/bottom 两种位置，净减约 12 行。

src/components/MatchResult.tsx

@@ -34,6 +34,8 @@ import { isRegistered } from "@/lib/userId";
 import ShareCardModal from "@/components/ShareCardModal";
 import RestaurantImage from "@/components/RestaurantImage";
 import AuthModal from "@/components/AuthModal";
+import Toast from "@/components/Toast";
+import { useToast } from "@/hooks/useToast";
 
 interface MatchResultProps {
   restaurant: Restaurant;
@@ -194,7 +196,7 @@ export default function MatchResult({
   const router = useRouter();
   const [showRunnerUps, setShowRunnerUps] = useState(false);
   const [showShareCard, setShowShareCard] = useState(false);
-  const [toast, setToast] = useState("");
+  const toast = useToast();
   const celebratedRef = useRef(false);
   const historySavedRef = useRef(false);
   const isSolo = userCount <= 1;
@@ -204,11 +206,6 @@ export default function MatchResult({
   const [registered, setRegistered] = useState(() => isRegistered());
   const [showAuth, setShowAuth] = useState(false);
 
-  const showToast = useCallback((msg: string) => {
-    setToast(msg);
-    setTimeout(() => setToast(""), 2200);
-  }, []);
-
   useEffect(() => {
     if (isUnanimous && !celebratedRef.current) {
       const timer = setTimeout(() => {
@@ -247,9 +244,9 @@ export default function MatchResult({
     (profile: UserProfile) => {
       setRegistered(true);
       setShowAuth(false);
-      showToast(`欢迎，${profile.username}！记录已保存`);
+      toast.show(`欢迎，${profile.username}！记录已保存`);
     },
-    [showToast],
+    [toast],
   );
 
   const handleFavorite = useCallback(async () => {
@@ -263,13 +260,13 @@ export default function MatchResult({
       });
       if (res.ok) {
         setFavorited(true);
-        showToast("已收藏");
+        toast.show("已收藏");
       }
     } catch {
       /* ignore */
     }
     setFavLoading(false);
-  }, [registered, userId, restaurant, favorited, favLoading, showToast]);
+  }, [registered, userId, restaurant, favorited, favLoading, toast]);
 
   if (matchType === "no_match") {
     return <NoMatchResult onReset={onReset} resetting={resetting} />;
@@ -635,22 +632,10 @@ export default function MatchResult({
           userCount,
           scene,
         }}
-        onToast={showToast}
+        onToast={toast.show}
       />
 
-      <AnimatePresence>
-        {toast && (
-          <motion.div
-            className="fixed left-1/2 top-10 z-60 -translate-x-1/2 rounded-xl bg-surface px-4 py-2.5 text-xs font-medium text-heading shadow-lg ring-1 ring-border"
-            initial={{ opacity: 0, y: -12, x: "-50%" }}
-            animate={{ opacity: 1, y: 0, x: "-50%" }}
-            exit={{ opacity: 0, y: -12, x: "-50%" }}
-            transition={{ type: "spring", stiffness: 400, damping: 25 }}
-          >
-            {toast}
-          </motion.div>
-        )}
-      </AnimatePresence>
+      <Toast message={toast.message} />
     </motion.div>
   );
 }

src/components/Toast.tsx

@@ -0,0 +1,34 @@
+"use client";
+
+import { motion, AnimatePresence } from "framer-motion";
+
+interface ToastProps {
+  message: string;
+  position?: "top" | "bottom";
+}
+
+const positionClass = {
+  top: "top-10",
+  bottom: "bottom-8",
+};
+
+export default function Toast({ message, position = "top" }: ToastProps) {
+  const isTop = position === "top";
+  const y = isTop ? -12 : 12;
+
+  return (
+    <AnimatePresence>
+      {message && (
+        <motion.div
+          className={`fixed left-1/2 z-60 -translate-x-1/2 rounded-xl bg-elevated px-4 py-2.5 text-xs font-medium text-heading shadow-lg ring-1 ring-subtle ${positionClass[position]}`}
+          initial={{ opacity: 0, y, x: "-50%" }}
+          animate={{ opacity: 1, y: 0, x: "-50%" }}
+          exit={{ opacity: 0, y, x: "-50%" }}
+          transition={{ type: "spring", stiffness: 400, damping: 25 }}
+        >
+          {message}
+        </motion.div>
+      )}
+    </AnimatePresence>
+  );
+}

src/components/TopNav.tsx

@@ -1,12 +1,13 @@
 "use client";
 
-import { useState, useCallback } from "react";
+import { useState } from "react";
 import { QrCode, LogOut, Crown, Lock } from "lucide-react";
-import { motion, AnimatePresence } from "framer-motion";
 import QrInviteModal from "./QrInviteModal";
 import RoomManageModal from "./RoomManageModal";
+import Toast from "@/components/Toast";
 import type { UserProfile, SceneType } from "@/types";
 import { getSceneConfig } from "@/lib/sceneConfig";
+import { useToast } from "@/hooks/useToast";
 
 interface TopNavProps {
   roomId: string;
@@ -36,15 +37,10 @@ export default function TopNav({
   scene = "eat",
 }: TopNavProps) {
   const sceneConfig = getSceneConfig(scene);
-  const [toast, setToast] = useState("");
+  const toast = useToast();
   const [showQr, setShowQr] = useState(false);
   const [showManage, setShowManage] = useState(false);
 
-  const showToast = useCallback((msg: string) => {
-    setToast(msg);
-    setTimeout(() => setToast(""), 2200);
-  }, []);
-
   return (
     <>
       <nav className="relative z-10 flex h-14 items-center px-4">
@@ -83,25 +79,13 @@ export default function TopNav({
         </h1>
       </nav>
 
-      <AnimatePresence>
-        {toast && (
-          <motion.div
-            className="fixed left-1/2 top-16 z-50 -translate-x-1/2 rounded-xl bg-elevated px-4 py-2.5 text-xs font-medium text-heading shadow-lg ring-1 ring-subtle"
-            initial={{ opacity: 0, y: -12, x: "-50%" }}
-            animate={{ opacity: 1, y: 0, x: "-50%" }}
-            exit={{ opacity: 0, y: -12, x: "-50%" }}
-            transition={{ type: "spring", stiffness: 400, damping: 25 }}
-          >
-            {toast}
-          </motion.div>
-        )}
-      </AnimatePresence>
+      <Toast message={toast.message} />
 
       <QrInviteModal
         open={showQr}
         onClose={() => setShowQr(false)}
         roomId={roomId}
-        onToast={showToast}
+        onToast={toast.show}
         scene={scene}
       />
 
@@ -116,7 +100,7 @@ export default function TopNav({
           swipeCounts={swipeCounts}
           totalCards={totalCards}
           userProfiles={userProfiles}
-          onToast={showToast}
+          onToast={toast.show}
         />
       )}
     </>