Add docker image build

SmartClinicManagementSystem/app/Dockerfile

@@ -0,0 +1,13 @@
+# Step 1: Use Maven with JDK 21 to build the app
+FROM gradle:8.14.3-jdk21-alpine AS builder
+WORKDIR /app
+COPY build.gradle .
+COPY src ./src
+RUN gradle clean bootJar -DskipTests
+
+# Step 2: Use lightweight JRE 21 for running the app
+FROM eclipse-temurin:21-jre-alpine-3.22
+WORKDIR /app
+COPY --from=builder /app/build/libs/app-1.0.0.jar app.jar
+EXPOSE 8080
+ENTRYPOINT ["java", "-jar", "app.jar"]