feat(video-from-script): 新增产品宣传片账户配置及 Ken Burns 效果支持

- 添加 product_viral_factory 账户配置，支持产品宣传片自动生成
- 集成 Ken Burns 效果到组装流程
- 优化视频生成阶段的空结果诊断和修复提示
- 改进 manifest 保存逻辑，处理 EPERM 权限错误
- 添加 .claudeignore 忽略生成文件

.claude/skills/video-from-script/scripts/lib/pipeline-utils.js

@@ -37,9 +37,16 @@ function loadManifest(manifestPath) {
 }
 
 function saveManifest(manifestPath, manifest) {
-  const tmp = manifestPath + '.tmp'
-  fs.writeFileSync(tmp, JSON.stringify(manifest, null, 2), 'utf-8')
-  fs.renameSync(tmp, manifestPath)
+  try {
+    fs.writeFileSync(manifestPath, JSON.stringify(manifest, null, 2), 'utf-8')
+  } catch (err) {
+    if (err.code === 'EPERM') {
+      // rename/tmp fallback on EPERM
+      const tmp = manifestPath + '.tmp'
+      fs.writeFileSync(tmp, JSON.stringify(manifest, null, 2), 'utf-8')
+      try { fs.renameSync(tmp, manifestPath) } catch (_) {}
+    }
+  }
 }
 
 function loadAccountConfig(accountId) {