chore: 添加双协议 LICENSE 配置

- 参考实现/代码: MIT (LICENSE)
- 课程文档: CC BY-SA 4.0 (LICENSE-docs)
- 新增根 README 说明授权分工

Co-authored-by: CommandCodeBot <noreply@commandcode.ai>

LICENSE

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+MIT License
+
+Copyright (c) 2026 Code-source-Lesson 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.

LICENSE-docs

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+本仓库课程文档采用 Creative Commons Attribution-ShareAlike 4.0 International (CC BY-SA 4.0) 许可。
+
+Course materials in this repository are licensed under CC BY-SA 4.0.
+
+完整协议文本 / Full license text:
+https://creativecommons.org/licenses/by-sa/4.0/legalcode
+
+中文摘要 / Human-readable summary:
+https://creativecommons.org/licenses/by-sa/4.0/deed.zh-hans
+
+你是自由的：
+- 共享 — 以任何媒介或格式复制、发行本作品
+- 演绎 — 修改、转换或以本作品为基础进行创作
+- 甚至用于商业目的
+
+惟须遵守下列条件：
+- 署名 — 你必须给出适当的署名，提供指向本许可协议的链接，同时标明是否对原始作品作了修改。
+- 相同方式共享 — 如果你再混合、转换或者基于本作品进行创作，你必须以与原作品相同的协议分发你的贡献。
+
+You are free to:
+- Share — copy and redistribute the material in any medium or format
+- Adapt — remix, transform, and build upon the material for any purpose, even commercially
+
+Under the following terms:
+- Attribution — You must give appropriate credit, provide a link to the license, and indicate if changes were made.
+- ShareAlike — If you remix, transform, or build upon the material, you must distribute your contributions under the same license as the original.

README.md

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+# Code-source-Lesson
+
+面向提高+ / 省选- 的信息学竞赛课程资料，覆盖图论、字符串、数据结构等 12 个主题，配套精选例题与 GNU C++17 参考实现。
+
+- 课程正文：[`课程/`](课程/README.md)
+- 参考实现：[`参考实现/`](参考实现/)
+- 选题范围：[`主题.md`](主题.md)
+
+## 许可 / License
+
+本仓库采用双协议：
+
+| 内容 | 路径 | 协议 |
+|---|---|---|
+| 课程文档 | `课程/`、`主题.md`、`AGENTS.md`、`README.md` | [CC BY-SA 4.0](LICENSE-docs) |
+| 参考实现代码 | `参考实现/`、`scripts/` | [MIT](LICENSE) |
+
+简言之：文档允许商用与二创，但二创须以相同协议共享；代码以 MIT 宽松许可，可自由商用与闭源引用。