文档：添加 MIT LICENSE 并优化 README

- 添加 MIT 开源许可证
- 精简 README.md 内容
- 完善项目描述

LICENSE

@@ -0,0 +1,21 @@
+MIT License
+
+Copyright (c) 2025 SRDB Contributors
+
+Permission is hereby granted, free of charge, to any person obtaining a copy
+of this software and associated documentation files (the "Software"), to deal
+in the Software without restriction, including without limitation the rights
+to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+copies of the Software, and to permit persons to whom the Software is
+furnished to do so, subject to the following conditions:
+
+The above copyright notice and this permission notice shall be included in all
+copies or substantial portions of the Software.
+
+THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
+SOFTWARE.

README.md

@@ -167,14 +167,10 @@ database_dir/
 ### 核心文档
 
 - [DOCS.md](DOCS.md) - 完整 API 文档和使用指南
-- [CLAUDE.md](CLAUDE.md) - 开发者指南和架构详解
+- [DESIGN.md](CLAUDE.md) - 数据库设计文档
-- [NULLABLE_GUIDE.md](NULLABLE_GUIDE.md) - Nullable 字段使用说明
 
 ### 示例教程
 
-- [Scan 方法指南](examples/scan_demo/README.md) - 扫描到结构体，支持 Object 和 Array
-- [所有类型示例](examples/all_types/) - 21 种类型的完整示例
-- [Nullable 示例](examples/nullable/) - Nullable 字段的使用
 - [WebUI 工具](examples/webui/README.md) - Web 管理界面
 
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