refactor: 删除 createPreview 调用，确认生成不再触发后端预览渲染

- 删除 createPreview API 导入和调用
- 预览已改为前端实时播放（Canvas + WebCodecs）
- taskId 改为直接使用 props.previewTaskId
- 移除 useCallback 依赖中的 selectedTemplate

apps/web/src/pages/generate/hooks/useGenerateVideo.ts

@@ -5,7 +5,7 @@
 import { useState, useCallback } from "react"
 import { message } from "antd"
 import type { GeneratedVideo } from "@/api/template-editor"
-import { confirmGeneration, createPreview } from "@/api/generation"
+import { confirmGeneration } from "@/api/generation"
 import type { UseGenerateVideoProps } from "./generate-video/types"
 import { getGenerationPhase } from "./generate-video/phase"
 import { useGenerationPolling } from "./generate-video/useGenerationPolling"
@@ -87,32 +87,10 @@ export function useGenerateVideo(props: UseGenerateVideoProps) {
         outputHeight = 1920
       }
 
-      // 获取或创建后端任务 ID
-      // 预览改为前端播放后，不再有预览任务，需要在此处创建
-      let taskId = props.previewTaskId
+      // 获取后端任务 ID（预览已改为前端实时播放，不再调用后端 createPreview）
+      const taskId = props.previewTaskId
       if (!taskId) {
-        const assetIds =
-          props.materialMode === "auto" ? props.smartSelectedIds : props.selectedMaterials
-        const previewResp = await createPreview({
-          template_id: selectedTemplate,
-          asset_ids: assetIds,
-          duration: props.duration || undefined,
-          video_ratio: props.videoRatio,
-          voice_ids: undefined,
-          title_config: props.titleSettings?.title
-            ? {
-                text: props.titleSettings.title,
-                font: props.titleSettings.font,
-                font_size: props.titleSettings.size,
-                font_color: props.titleSettings.color,
-                position: props.titleSettings.position,
-                bold: props.titleSettings.bold,
-                stroke: props.titleSettings.stroke,
-                shadow: props.titleSettings.shadow,
-              }
-            : undefined,
-        })
-        taskId = previewResp.task_id
+        throw new Error("缺少预览任务 ID，无法确认生成")
       }
 
       await confirmGeneration(taskId, {
@@ -132,7 +110,7 @@ export function useGenerateVideo(props: UseGenerateVideoProps) {
       setGenerateError(finalMsg)
       message.error(finalMsg)
     }
-  }, [props, clearTimer, startPolling, selectedTemplate])
+  }, [props, clearTimer, startPolling])
 
   /* 重新生成（失败后重试） */
   const retry = useCallback(() => {