Document frontend component structure

- Add docs/component-structure.md covering the current React component hierarchy, page routes, public components, API/Auth/Utils boundaries, and data flow.

- Document the internal responsibilities and split risks for large pages including ReportEditor and TemplateManage.

- Link the new component structure guide from README, docs index, AGENTS file tree, and progress notes.

README.md

@@ -182,6 +182,7 @@ cp .env.example .env.local
 - [docs/installation.md](./docs/installation.md)：安装、初始设置和首次验收。
 - [docs/requirements.md](./docs/requirements.md)：需求文档。
 - [docs/design.md](./docs/design.md)：设计文档。
+- [docs/component-structure.md](./docs/component-structure.md)：前端组件结构和拆分边界。
 - [docs/features.md](./docs/features.md)：功能真实性盘点。
 - [docs/testing.md](./docs/testing.md)：测试文档。
 - [docs/data-storage.md](./docs/data-storage.md)：本地数据存储说明。