Preserve frame position order for auto insertion

- Allow system frame position percentages to keep two decimal places without reordering saved values.

- Stop frontend and backend settings normalization from sorting framePositions on load or save.

- Capture automatic video frames in timeline order while retaining each configured position index.

- Insert automatically selected frames into report placeholders according to the configured percentage order.

- Add frame position utilities and unit coverage for two-decimal rounding, clamping, order preservation, and timeline capture planning.

- Update README, AGENTS, feature, requirement, report editor, system settings, progress, and testing docs for the new frame ordering behavior.

README.md

@@ -202,6 +202,7 @@ cp .env.example .env.local
 - 默认报告模板结构和字段配置。
 - 模板 HTML 导出包字段库元数据。
 - AI 区域扫描和报告编辑器加载后同步。
+- 抽帧百分比两位小数、保序和按时间截图计划。
 - 打印导出入口。
 - 后端权限策略、AI 入参和语音代理帧处理。