docs: fix license to BSD 2-Clause and add sponsor section

- Correct license from MIT to BSD 2-Clause in all README files
- Add sponsor section with GitHub Sponsors link

Author: yhk1038

README.ja.md

@@ -279,6 +279,16 @@ watch:
 
 コントリビューションを歓迎します！Issue や Pull Request をお気軽にお送りください。
 
+## ❤️ T-Ruby を支援する
+
+T-Ruby が役立つと思ったら、プロジェクトの継続的な開発と実験を支援するためにスポンサーをご検討ください。
+
+<p align="center">
+  <a href="https://github.com/sponsors/type-ruby">
+    <img src="https://img.shields.io/badge/Sponsor-❤️-ea4aaa" alt="Sponsor" />
+  </a>
+</p>
+
 ## ライセンス
 
-[MIT](./LICENSE)
+[BSD 2-Clause](./LICENSE)

README.ko.md

@@ -279,6 +279,16 @@ watch:
 
 기여를 환영합니다! 이슈와 풀 리퀘스트를 자유롭게 제출해 주세요.
 
+## ❤️ T-Ruby 후원하기
+
+T-Ruby가 유용하다면, 프로젝트의 지속적인 개발과 실험을 위해 후원을 고려해 주세요.
+
+<p align="center">
+  <a href="https://github.com/sponsors/type-ruby">
+    <img src="https://img.shields.io/badge/Sponsor-❤️-ea4aaa" alt="Sponsor" />
+  </a>
+</p>
+
 ## 라이선스
 
-[MIT](./LICENSE)
+[BSD 2-Clause](./LICENSE)

README.md

@@ -284,6 +284,16 @@ See [ROADMAP.md](./ROADMAP.md) for details.
 
 Contributions are welcome! Please feel free to submit issues and pull requests.
 
+## ❤️ Support T-Ruby
+
+If you find T-Ruby useful, consider sponsoring the project to support ongoing development and experimentation.
+
+<p align="center">
+  <a href="https://github.com/sponsors/type-ruby">
+    <img src="https://img.shields.io/badge/Sponsor-❤️-ea4aaa" alt="Sponsor" />
+  </a>
+</p>
+
 ## License
 
-[MIT](./LICENSE)
+[BSD 2-Clause](./LICENSE)