feat(video-pipeline): 支持滤镜和转场从账号配置继承

- 新增 Q18 滤镜和 Q19 转场字段到账号创建参考文档
- 重构账号配置加载函数为通用 `loadAccountConfig`，支持读取滤镜和转场
- `capcut_assemble.js` 支持 CLI 参数优先、账号配置兜底的滤镜/特效继承逻辑
- 模板 `account.json` 将闭幕转场从 "黑场" 修正为 "闪黑

accounts/_template/account.json

@@ -40,12 +40,12 @@
         "hook":    { "name": "闪白", "duration": 100000 },
         "keypoint": { "name": "闪白", "duration": 120000 },
         "body":    { "name": "溶解", "duration": 300000 },
-        "closing": { "name": "黑场", "duration": 200000 }
+        "closing": { "name": "闪黑", "duration": 200000 }
       },
       "byDirector": {
         "tarantino": { "name": "闪白", "duration": 100000 },
         "kitano":    { "name": "溶解", "duration": 400000 },
-        "fincher":   { "name": "黑场", "duration": 200000 }
+        "fincher":   { "name": "闪黑", "duration": 200000 }
       }
     }
   }

accounts/军事账号/account.json

@@ -21,7 +21,7 @@
   "videoStylePrompt": "prompts/视频提示词.md",
   "capcut": {
     "effects": ["录制边框 III"],
-    "filter": "电影感:40",
+    "filter": "质感电影:40",
     "subtitleStyle": {
       "font": "思源黑体 Heavy",
       "fontSize": 24,
@@ -55,12 +55,12 @@
         "hook":     { "name": "闪白", "duration": 100000 },
         "keypoint": { "name": "闪白", "duration": 120000 },
         "body":     { "name": "溶解", "duration": 300000 },
-        "closing":  { "name": "黑场", "duration": 200000 }
+        "closing":  { "name": "闪黑", "duration": 200000 }
       },
       "byDirector": {
         "tarantino": { "name": "闪白", "duration": 100000 },
         "kitano":    { "name": "溶解", "duration": 400000 },
-        "fincher":   { "name": "黑场", "duration": 200000 }
+        "fincher":   { "name": "闪黑", "duration": 200000 }
       }
     }
   }