修复演示恢复项目帧数据

- 恢复演示出厂设置后直接解析演视LC视频序列并生成可打开帧序列

- 保持演视DICOM序列按文件名自然顺序恢复并生成帧

- 增加 MinIO 浏览器访问端点配置，修复 Docker 部署中封面和帧图预签名地址使用容器内主机名的问题

- 更新管理员恢复测试覆盖视频和 DICOM 帧数量

- 更新 README 和前后端契约/设计/测试文档中的演示恢复说明

backend/main.py

@@ -71,7 +71,7 @@ def _seed_default_project_sync() -> None:
         LEGACY_DEMO_DICOM_PROJECT_NAMES,
         LEGACY_DEMO_VIDEO_PROJECT_NAMES,
         create_parsed_dicom_demo_project,
-        create_unparsed_video_demo_project,
+        create_parsed_video_demo_project,
         demo_dicom_files,
     )
 
@@ -96,7 +96,7 @@ def _seed_default_project_sync() -> None:
             db.commit()
         existing_video = db.query(Project).filter(Project.name == DEMO_VIDEO_PROJECT_NAME).first()
         if existing_video is None and os.path.exists(settings.demo_video_path):
-            video_project = create_unparsed_video_demo_project(
+            video_project = create_parsed_video_demo_project(
                 db,
                 owner=admin,
                 video_path=settings.demo_video_path,