refactor: remove legacy RuoYi artifacts and unused dependencies
- Delete old RuoYi scripts: bin/*.bat, ry.bat, ry.sh
- Delete empty directories: controller/, service/impl/, static/, templates/
- Delete unused mybatis-config.xml (Spring Boot auto-configures MyBatis)
- Remove unused Maven dependencies: fastjson2, poi-ooxml
- Clean root pom.xml: remove bitwalker, kaptcha, oshi, velocity, poi, fastjson2 version management
Build verified: mvn clean package passes.