fix: 修复前端代码质量问题

- 创建 Toast 通知组件，替换所有 alert() 调用
- 修复 useReview hook 内存泄漏（setInterval 清理）
- 移除所有 console.error 和 console.log 语句
- 为复制操作失败添加用户友好的 toast 提示

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

frontend/hooks/useReview.ts

@@ -1,6 +1,6 @@
 'use client'
 
-import { useState, useCallback, useEffect } from 'react'
+import { useState, useCallback, useEffect, useRef } from 'react'
 import { api } from '@/lib/api'
 import type {
   VideoReviewRequest,
@@ -24,6 +24,7 @@ export function useReview(options: UseReviewOptions = {}) {
   const [isPolling, setIsPolling] = useState(false)
   const [task, setTask] = useState<ReviewTask | null>(null)
   const [error, setError] = useState<Error | null>(null)
+  const intervalRef = useRef<NodeJS.Timeout | null>(null)
 
   /**
    * 提交审核
@@ -97,10 +98,22 @@ export function useReview(options: UseReviewOptions = {}) {
     }
   }, [task?.createdAt])
 
+  /**
+   * 清除轮询定时器
+   */
+  const clearPollingInterval = useCallback(() => {
+    if (intervalRef.current) {
+      clearInterval(intervalRef.current)
+      intervalRef.current = null
+    }
+  }, [])
+
   /**
    * 开始轮询进度
    */
   const startPolling = useCallback((reviewId: string) => {
+    // 清除之前的轮询（如果有）
+    clearPollingInterval()
     setIsPolling(true)
 
     const poll = async () => {
@@ -108,36 +121,45 @@ export function useReview(options: UseReviewOptions = {}) {
         const progress = await fetchProgress(reviewId)
 
         if (progress.status === 'completed') {
+          clearPollingInterval()
           setIsPolling(false)
           const result = await fetchResult(reviewId)
           onComplete?.(result)
         } else if (progress.status === 'failed') {
+          clearPollingInterval()
           setIsPolling(false)
           const error = new Error('审核失败')
           setError(error)
           onError?.(error)
         }
-      } catch (err) {
+      } catch {
         // 继续轮询，忽略单次错误
-        console.error('Polling error:', err)
       }
     }
 
-    const intervalId = setInterval(poll, pollingInterval)
+    intervalRef.current = setInterval(poll, pollingInterval)
     poll() // 立即执行一次
 
     return () => {
-      clearInterval(intervalId)
+      clearPollingInterval()
       setIsPolling(false)
     }
-  }, [fetchProgress, fetchResult, pollingInterval, onComplete, onError])
+  }, [fetchProgress, fetchResult, pollingInterval, onComplete, onError, clearPollingInterval])
 
   /**
    * 停止轮询
    */
   const stopPolling = useCallback(() => {
+    clearPollingInterval()
     setIsPolling(false)
-  }, [])
+  }, [clearPollingInterval])
+
+  // 组件卸载时清除定时器，防止内存泄漏
+  useEffect(() => {
+    return () => {
+      clearPollingInterval()
+    }
+  }, [clearPollingInterval])
 
   /**
    * 重置状态