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

Dockerfile

@@ -1,8 +1,18 @@
+FROM gradle:8.14-jdk21 AS build
+
+WORKDIR /app
+
+COPY build.gradle settings.gradle ./
+COPY gradle ./gradle
+COPY src ./src
+
+RUN gradle clean build -x test --no-daemon
+
 FROM eclipse-temurin:21-jre-alpine
 
 WORKDIR /app
 
-COPY build/libs/*.jar app.jar
+COPY --from=build /app/build/libs/*.jar app.jar
 
 EXPOSE 8080