fix: Step5 标题样式实时预览 - 修复 useMemo 依赖项问题

问题：调整字体样式时，标题不会实时更新
根因：useMemo 依赖项为 [titleSettings] 对象引用，React 无法正确检测到属性变化

修复：
- 将 useMemo 依赖改为明确的属性列表 [font, size, color, bold, italic, stroke, shadow]
- 添加 eslint-disable 注释抑制误报警告

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

@@ -115,7 +115,20 @@ const TitleOverlay: React.FC<{ titleSettings: TitleSettings }> = ({ titleSetting
     () => getPositionStyle(titleSettings.position),
     [titleSettings.position],
   )
-  const titleStyle = useMemo(() => buildTitleStyle(titleSettings), [titleSettings])
+  // eslint-disable-next-line react-hooks/exhaustive-deps
+  const titleStyle = useMemo(
+    () => buildTitleStyle(titleSettings),
+    // eslint-disable-next-line react-hooks/exhaustive-deps
+    [
+      titleSettings.font,
+      titleSettings.size,
+      titleSettings.color,
+      titleSettings.bold,
+      titleSettings.italic,
+      titleSettings.stroke,
+      titleSettings.shadow,
+    ],
+  )
 
   if (!titleSettings.title?.trim()) return null