fix: switch Dockerfile from Alpine to Ubuntu for ONNX/DJL

rag-service/docker/Dockerfile

@@ -1,5 +1,5 @@
 # Stage 1: Build
-FROM eclipse-temurin:25-jdk-alpine AS build
+FROM eclipse-temurin:25-jdk AS build
 WORKDIR /app
 COPY ../pom.xml .
 COPY ../.mvn .mvn
@@ -9,11 +9,11 @@ COPY ../src src
 RUN ./mvnw package -DskipTests -B
 
 # Stage 2: Run
-FROM eclipse-temurin:25-jdk-alpine
+FROM eclipse-temurin:25-jre
 WORKDIR /app
-RUN addgroup -S appgroup && adduser -S appuser -G appgroup
+RUN groupadd -r appgroup && useradd -r -g appgroup appuser
 COPY --from=build /app/target/*.jar app.jar
 RUN chown appuser:appgroup app.jar
 USER appuser
-EXPOSE 8080
+EXPOSE 8081
 ENTRYPOINT ["java", "-jar", "app.jar"]