fix(room): auto-redirect to room when user already in room

- Add auto-redirect logic in HomePage when user.currentRoomId exists
- Add error handling in RoomPage to clear stale room state
- Ensure socket reconnection works after page refresh
- Fix "您已在房间中，请先退出当前房间" error on refresh

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

Author: dongmucat

frontend/src/pages/home/index.tsx

@@ -1,4 +1,4 @@
-import { useState } from 'react'
+import { useState, useEffect } from 'react'
 import { useNavigate } from 'react-router'
 import { motion, AnimatePresence } from 'framer-motion'
 import { BookOpen } from 'lucide-react'
@@ -16,6 +16,13 @@ export default function HomePage() {
   const [localError, setLocalError] = useState('')
   const [showRules, setShowRules] = useState(false)
 
+  // 如果用户已在房间中，自动跳转到该房间
+  useEffect(() => {
+    if (user?.currentRoomId) {
+      navigate(`/room/${user.currentRoomId}`, { replace: true })
+    }
+  }, [user?.currentRoomId, navigate])
+
   const handleCreateRoom = async () => {
     setLocalError('')
     try {

frontend/src/pages/room/index.tsx

@@ -132,6 +132,20 @@ export default function RoomPage() {
     }
   }, [roomId, fetchRoomInfo])
 
+  // 如果房间不存在，清除用户状态并返回首页
+  useEffect(() => {
+    if (error && !isLoading && !room) {
+      const user = useAuthStore.getState().user
+      if (user?.currentRoomId === roomId) {
+        useAuthStore.setState({
+          user: { ...user, currentRoomId: null }
+        })
+      }
+      toast('房间不存在或已关闭')
+      navigate('/', { replace: true })
+    }
+  }, [error, isLoading, room, roomId, navigate])
+
   useEffect(() => {
     if (roomId && token && !connectedRef.current) {
       connect(token, roomId)