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>

accounts/product_viral_factory/account.json

@@ -0,0 +1,53 @@
+{
+  "id": "product_viral_factory",
+  "name": "产品宣传片",
+  "description": "PPT内容/卖点 → 结构化解析 → 分镜脚本 → 图片提示词 → 生图 → AI视频 → 成片，支持无风格参考图时由产品图自动派生风格",
+  "defaultFormat": "9:16",
+  "imageModel": "gemini",
+  "videoModel": "veo3-fast",
+  "batchSize": 30,
+  "ttsVoice": "",
+  "ttsInstruction": "",
+  "storyboardPrompt": "prompts/产品分镜.md",
+  "imageStylePrompt": "prompts/图片提示词.md",
+  "videoStylePrompt": "prompts/视频提示词.md",
+  "references": [],
+  "referenceMode": "product-as-style",
+  "referenceModeNote": "优先使用references中的风格参考图；无风格图时，由产品参考图自动派生光影/构图/背景风格",
+  "capcut": {
+    "effects": [],
+    "filter": "",
+    "subtitleStyle": {
+      "fontSize": 12,
+      "color": "#FFFFFF",
+      "highlightColor": "#FF6B35",
+      "bold": true
+    },
+    "keywordStyle": {
+      "textEffect": "简约白色黑边花字",
+      "fontSize": 60,
+      "color": "#FFFFFF",
+      "bold": true,
+      "transformY": 0,
+      "inAnimation": "打字机效果",
+      "outAnimation": "模糊淡出",
+      "inAnimDuration": 300000,
+      "outAnimDuration": 300000
+    },
+    "defaultBGM": "",
+    "transitions": {
+      "strategy": "rhythm",
+      "default": { "name": "溶解", "duration": 400000 },
+      "byPosition": {
+        "hook":    { "name": "闪白", "duration": 100000 },
+        "keypoint": { "name": "闪白", "duration": 150000 },
+        "body":    { "name": "溶解", "duration": 400000 },
+        "closing": { "name": "闪黑", "duration": 300000 }
+      }
+    },
+    "kenBurns": {
+      "enabled": true,
+      "default": { "startScale": 1.0, "scaleRate": 0.7, "panXRate": 0, "panYRate": 0 }
+    }
+  }
+}