Sync inserted AI regions immediately

- Track report editor AI regions in React state instead of only scanning contentEditable DOM during render.

- Observe editor AI region mutations and refresh the AI writing target dropdown without requiring page navigation or refresh.

- Select newly inserted AI regions immediately after insertion and keep a live DOM fallback for generation.

- Harden AI region insertion so it still appends the region if execCommand has no active editor selection.

- Escape AI region names before injecting template HTML and add an accessible label for the insert button.

- Add Playwright coverage for inserting an AI region and seeing it immediately in the AI writing dropdown.

- Update report editor, feature, progress, testing, and AGENTS documentation for AI region synchronization.

docs/modules/report-editor.md

@@ -71,6 +71,8 @@ AI 面板支持两种模式：
 - 对话模式：根据当前报告内容和图片上下文回答问题。
 - 修改模式：选中 `.ai-region` 后要求模型返回 JSON，其中包含 `reply` 和 `updatedHtml`。
 
+编辑器会监听正文中的 `.ai-region` 变化；用户插入新的 AI 可编辑区域后，AI 撰写面板的目标下拉栏会立即更新，不需要离开页面或刷新。
+
 模型返回 HTML 后，系统会清理换行和 `<br>`，生成差异预览。用户确认后才写入目标 `.ai-content`。
 
 当前 AI 调用使用后端代理：