Add Docker configuration and .dockerignore for Serena application

Dockerfile

@@ -0,0 +1,65 @@
+# Multi-stage Dockerfile for Serena (Backend + Frontend)
+
+# Stage 1: Build Frontend
+FROM node:18-alpine AS frontend-builder
+
+WORKDIR /app/frontend
+
+# Copy package files
+COPY frontend/package*.json ./
+
+# Install dependencies
+RUN npm ci --only=production
+
+# Copy frontend source
+COPY frontend/ ./
+
+# Build frontend
+RUN npm run build
+
+# Stage 2: Build Backend
+FROM openjdk:21-jdk-slim AS backend-builder
+
+WORKDIR /app/backend
+
+# Copy Gradle wrapper and build files
+COPY backend/gradlew ./
+COPY backend/gradle/ ./gradle/
+COPY backend/build.gradle ./
+COPY backend/settings.gradle ./
+
+# Copy source code
+COPY backend/src/ ./src/
+
+# Make gradlew executable and build
+RUN chmod +x gradlew
+RUN ./gradlew build --no-daemon -x test
+
+# Stage 3: Runtime
+FROM openjdk:21-jre-slim
+
+WORKDIR /app
+
+# Install curl for health checks
+RUN apt-get update && apt-get install -y curl && rm -rf /var/lib/apt/lists/*
+
+# Copy built backend JAR
+COPY --from=backend-builder /app/backend/build/libs/*.jar app.jar
+
+# Copy built frontend (will be served by Spring Boot)
+COPY --from=frontend-builder /app/frontend/build/ /app/static/
+
+# Create non-root user
+RUN groupadd -r serena && useradd -r -g serena serena
+RUN chown -R serena:serena /app
+USER serena
+
+# Expose port
+EXPOSE 8080
+
+# Health check
+HEALTHCHECK --interval=30s --timeout=10s --start-period=60s --retries=3 \
+  CMD curl -f http://localhost:8080/actuator/health || exit 1
+
+# Run the application
+ENTRYPOINT ["java", "-jar", "app.jar"]