fix: resolve TypeScript compile errors in PreviewVideoPanel

- PreviewVideoPanel.tsx: remove duplicate showTitlePreview declaration
  (removed from props interface and destructure, kept const assignment)
- PreviewVideoPanel.tsx: add missing import for TitlePreviewCanvas
- Step4TitleSettings.tsx: remove unused TitlePreviewCanvas import
  (component migrated to PreviewVideoPanel)

apps/web/src/pages/generate/components/PreviewVideoPanel.tsx

@@ -16,6 +16,7 @@ import { PlayCircleOutlined, LoadingOutlined } from "@ant-design/icons"
 import type { PreviewResult, PreviewStatus } from "../hooks/useStep5Preview"
 import type { TitleSettings } from "../types"
 import { drawTitleOnCanvas } from "../utils/drawTitleOnCanvas"
+import TitlePreviewCanvas from "./title/TitlePreviewCanvas"
 
 interface PreviewVideoPanelProps {
   previewStatus: PreviewStatus
@@ -28,8 +29,6 @@ interface PreviewVideoPanelProps {
   titleText?: string
   /** 标题样式设置 */
   titleSettings?: TitleSettings
-  /** Step4 标题预览模式 */
-  showTitlePreview?: boolean
   /** 素材视频 URL（用于 Step4 标题预览背景） */
   sourceVideoUrl?: string
 }
@@ -45,7 +44,6 @@ export const PreviewVideoPanel: React.FC<PreviewVideoPanelProps> = ({
   onRegenerate,
   titleText,
   titleSettings,
-  showTitlePreview,
   sourceVideoUrl,
 }) => {
   const hasPreview = previewStatus === "ready" && previewResult

apps/web/src/pages/generate/components/Step4TitleSettings.tsx

@@ -8,7 +8,6 @@ import type { TitleSettings } from "../types"
 import { useStep4Title } from "../hooks/useStep4Title"
 import AiTitleGenerator from "./title/AiTitleGenerator"
 import TitleStylePanel from "./title/TitleStylePanel"
-import TitlePreviewCanvas from "./title/TitlePreviewCanvas"
 
 interface Step4TitleSettingsProps {
   titleSettings: TitleSettings