Add installation and initial setup documentation

- Add docs/installation.md covering prerequisites, port usage, Docker startup, local development setup, default accounts, first-run validation, and common setup issues.

- Link the installation guide from the project README and docs index.

- Point deployment documentation to the installation guide for first-time setup.

- Update AGENTS.md and progress documentation to include the new installation guide.

README.md

@@ -19,6 +19,8 @@
 
 更细的功能真实性判断见 [docs/features.md](./docs/features.md)。
 
+首次安装、端口规划、数据库初始化和常见问题见 [docs/installation.md](./docs/installation.md)。
+
 ## 技术栈
 
 - React 19
@@ -177,6 +179,7 @@ cp .env.example .env.local
 ## 文档
 
 - [docs/README.md](./docs/README.md)：文档入口。
+- [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/features.md](./docs/features.md)：功能真实性盘点。