Add USER directive in Dockerfile

- Set USER to 1000 for improved security and permissions

Author: PatrickZdarsky

shiftservice/Dockerfile

@@ -25,5 +25,6 @@ FROM docker.io/eclipse-temurin:25-jre-alpine AS server
 WORKDIR /app
 COPY --from=builder /app/shiftservice/target/shiftservice-*.jar /app/app.jar
 
+USER 1000
 EXPOSE 8080
 CMD ["java", "-jar", "app.jar"]