feat: 视频阶段诊断增强 + 新账号 product_viral_factory + 执黑先行提示词更新

- phase-videos.js: 增加 item 不符合条件时的逐项诊断日志，明确 confirmed 校验
- pipeline-utils.js: saveManifest 先直写，EPERM 时回退 tmp+rename
- 执黑先行: 分镜/图片/视频提示词完善
- 新增 product_viral_factory 账号（PPT产品宣传片方向）

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

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

@@ -27,9 +27,16 @@ 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) {