feat(scaffold): add Dockerfile [skip ci]

Dockerfile

@@ -0,0 +1,30 @@
+# ---- Build stage ----
+FROM maven:3.9-eclipse-temurin-17-alpine AS build
+WORKDIR /workspace
+
+COPY pom.xml .
+RUN mvn dependency:go-offline -q
+
+COPY src ./src
+RUN mvn package -DskipTests -q
+
+# ---- Runtime stage ----
+FROM eclipse-temurin:17-jre-alpine
+WORKDIR /app
+
+# Download OTel Java agent for zero-code auto-instrumentation
+RUN wget -q -O /app/otel-agent.jar \
+    "https://github.com/open-telemetry/opentelemetry-java-instrumentation/releases/download/v2.5.0/opentelemetry-javaagent.jar"
+
+# Non-root user
+RUN addgroup -S appgroup && adduser -S appuser -G appgroup
+USER appuser
+
+COPY --from=build /workspace/target/*.jar app.jar
+
+EXPOSE 8080
+
+HEALTHCHECK --interval=30s --timeout=5s --start-period=30s --retries=3 \
+    CMD wget -qO- http://localhost:8080/actuator/health | grep -q '"status":"UP"' || exit 1
+
+ENTRYPOINT ["java", "-javaagent:/app/otel-agent.jar", "-jar", "app.jar"]