feat: complete todo backend with monitoring

- Spring Boot REST API with CRUD operations
- PostgreSQL with HikariCP connection pool
- Multi-stage Docker build (Gradle 8.14 + JRE Alpine)
- Docker Compose orchestration
- Prometheus metrics collection
- Grafana dashboards (app & database)
- Clean layered architecture (Entity/Repository/Service/Controller/DTO)
- Global exception handling
- Actuator health checks

.gitignore

@@ -1,4 +1,3 @@
-HELP.md
 .gradle
 build/
 !gradle/wrapper/gradle-wrapper.jar
@@ -35,3 +34,6 @@ out/
 
 ### VS Code ###
 .vscode/
+
+### Docker ###
+*.jar