docs: update README, API reference, dev-log, project structure with Agent monitoring + quick-alarm + latest fixes

- README.md: React 19, default pwd 123456, Docker Compose deploy, correct module list
- api-reference.md: add Agent monitoring section (report/latest/rules/quick-setup/alerts/tasks/kline)
- dev-log.md: new entry documenting hostname/IP fix, system collector, offline detection, quick alarm
- project-structure.md: add agent/ directory, dev-log.md link, React 19

docs/README.md

@@ -12,6 +12,7 @@
 | [数据库设计](./database-schema.md) | 数据模型和表结构 |
 | [开发规范](./development-guide.md) | 代码规范、Git 工作流 |
 | [部署指南](./deployment.md) | 生产环境部署 |
+| [开发日志](./dev-log.md) | 详细开发日志（按日期记录） |
 
 ## 设计文档