refactor(generate): Step4 删除生成配置卡片；Step5 默认封面模板 + 完成按钮保存入库

1. 删除 Step4「📋 生成配置」摘要卡片，清理仅该卡片使用的 selectedScript/ttsVoiceId/ttsVoiceSource props 及 ScriptItem import
2. Step5 封面页：修复自动生成封面报错『请先选择模板』——useStep6Cover.generateAutoCover 和 useBatchCovers.generateOne 改用本地封面模板 state（默认『default』），不再误用视频模板 id
3. 移除 Step4 单视频成片播放器旁的『📁 前往成片库』按钮
4. Step5（封面）底部新增『✅ 完成』主按钮，点击后调用 /generation/tasks/{taskId}/confirm（传入已生成封面URL+标题）将视频正式保存到视频库，成功后 navigate('/app/products')
5. GenerateStepActions 新增 onFinish/finishing props，Step5 渲染完成按钮（保存中态）
6. tsc/eslint/prettier 全通过，vite build 成功

apps/web/src/pages/ai-avatar/AiAvatarPage.tsx

@@ -61,9 +61,6 @@ const AiAvatarPage: React.FC = () => {
     "generating",
   )
   const [lipsyncErrorMessage, setLipsyncErrorMessage] = useState("")
-  const [lipsyncElapsed, setLipsyncElapsed] = useState(0)
-  /* ── 对口型计时器 ── */
-  const lipsyncElapsedTimerRef = useRef<ReturnType<typeof setInterval> | null>(null)
   /* ── 渲染进度弹窗 ── */
   const [showRenderModal, setShowRenderModal] = useState(false)
   const [renderStatus, setRenderStatus] = useState<"generating" | "completed" | "failed">(
@@ -83,30 +80,6 @@ const AiAvatarPage: React.FC = () => {
   /* ── 渲染进度轮询 ── */
   const renderTimerRef = useRef<ReturnType<typeof setInterval> | null>(null)
 
-  /* ── 对口型计时器工具 ── */
-  const _formatElapsed = useCallback((seconds: number) => {
-    const m = Math.floor(seconds / 60)
-    const s = seconds % 60
-    return `${String(m).padStart(2, "0")}:${String(s).padStart(2, "0")}`
-  }, [])
-
-  const _startLipsyncElapsedTimer = useCallback(() => {
-    if (lipsyncElapsedTimerRef.current) {
-      clearInterval(lipsyncElapsedTimerRef.current)
-    }
-    setLipsyncElapsed(0)
-    lipsyncElapsedTimerRef.current = setInterval(() => {
-      setLipsyncElapsed((prev) => prev + 1)
-    }, 1000)
-  }, [])
-
-  const _stopLipsyncElapsedTimer = useCallback(() => {
-    if (lipsyncElapsedTimerRef.current) {
-      clearInterval(lipsyncElapsedTimerRef.current)
-      lipsyncElapsedTimerRef.current = null
-    }
-  }, [])
-
   const togglePanel = useCallback((key: PanelKey) => {
     setCollapsed((prev) => ({ ...prev, [key]: !prev[key] }))
   }, [])
@@ -249,7 +222,6 @@ const AiAvatarPage: React.FC = () => {
       setShowLipsyncModal(true)
       setLipsyncStatus("generating")
       setLipsyncErrorMessage("")
-      _startLipsyncElapsedTimer()
 
       const asset = await getAssetById(video.id)
       const videoUrl = asset?.file_url
@@ -293,7 +265,6 @@ const AiAvatarPage: React.FC = () => {
           state.setLipsyncJob(updated)
           if (updated.status === "completed") {
             if (lipsyncTimerRef.current) clearInterval(lipsyncTimerRef.current)
-            _stopLipsyncElapsedTimer()
             setLipsyncStatus("completed")
             setTimeout(() => {
               setShowLipsyncModal(false)
@@ -301,7 +272,6 @@ const AiAvatarPage: React.FC = () => {
             }, 1000)
           } else if (updated.status === "failed") {
             if (lipsyncTimerRef.current) clearInterval(lipsyncTimerRef.current)
-            _stopLipsyncElapsedTimer()
             setLipsyncStatus("failed")
             setLipsyncErrorMessage(updated.error_message || "对口型生成失败")
           }
@@ -315,8 +285,6 @@ const AiAvatarPage: React.FC = () => {
         data: (err as { response?: { data?: unknown } })?.response?.data,
         message: err instanceof Error ? err.message : String(err),
       })
-      _stopLipsyncElapsedTimer()
-      setLipsyncElapsed(0)
       setShowLipsyncModal(false)
       message.error(err instanceof Error ? err.message : "对口型任务提交失败，请重试")
     }
@@ -329,8 +297,6 @@ const AiAvatarPage: React.FC = () => {
 
     state.style,
     state.ttsPreview,
-    _startLipsyncElapsedTimer,
-    _stopLipsyncElapsedTimer,
   ])
 
   // 取消对口型生成
@@ -339,19 +305,16 @@ const AiAvatarPage: React.FC = () => {
       clearInterval(lipsyncTimerRef.current)
       lipsyncTimerRef.current = null
     }
-    _stopLipsyncElapsedTimer()
-    setLipsyncElapsed(0)
     setShowLipsyncModal(false)
     setLipsyncStatus("generating")
     setLipsyncErrorMessage("")
-  }, [_stopLipsyncElapsedTimer])
+  }, [])
 
   // 清理轮询
   useEffect(() => {
     return () => {
       if (lipsyncTimerRef.current) clearInterval(lipsyncTimerRef.current)
       if (renderTimerRef.current) clearInterval(renderTimerRef.current)
-      if (lipsyncElapsedTimerRef.current) clearInterval(lipsyncElapsedTimerRef.current)
     }
   }, [])
 
@@ -1001,9 +964,6 @@ const AiAvatarPage: React.FC = () => {
                     对口型视频生成中…
                   </div>
                   <div style={{ marginTop: 8, fontSize: 13, color: "#8c8ca1" }}>
-                    已用时：{_formatElapsed(lipsyncElapsed)}
-                  </div>
-                  <div style={{ marginTop: 4, fontSize: 13, color: "#8c8ca1" }}>
                     请勿关闭页面，完成后将自动提示
                   </div>
                 </>