feat: Introduce application version display in the frontend footer, showing both frontend and backend versions with integrated build arguments.

backend/Dockerfile

@@ -8,6 +8,8 @@ RUN mvn clean package -DskipTests
 # Run stage
 FROM eclipse-temurin:25-jre
 WORKDIR /app
+ARG APP_VERSION=dev
+ENV APP_VERSION=${APP_VERSION}
 COPY --from=build /app/target/*.jar app.jar
 EXPOSE 8080
 ENTRYPOINT ["java", "-jar", "app.jar"]