fix: resolve Docker build failures and optimise backend image build

.github/workflows/ci-cd.yml

@@ -167,25 +167,14 @@ jobs:
       - name: Checkout repository
         uses: actions/checkout@v4
 
-      - name: Download backend JAR
-        uses: actions/download-artifact@v4
-        with:
-          name: backend-jar
-          path: backend/target/
-
-      - name: Download frontend dist
-        uses: actions/download-artifact@v4
-        with:
-          name: frontend-dist
-          path: frontend/dist/
-
       - name: Set up Docker Buildx
         uses: docker/setup-buildx-action@v3
 
       - name: Build backend image
         uses: docker/build-push-action@v5
         with:
-          context: backend
+          context: .
+          file: backend/Dockerfile
           push: false
           tags: toyswap-backend:${{ github.sha }}
           outputs: type=docker,dest=/tmp/backend-image.tar

backend/Dockerfile

@@ -1,10 +1,12 @@
 # Stage 1: Build (only if JAR not already provided by CI)
 FROM eclipse-temurin:17-jdk-alpine AS build
 WORKDIR /app
-COPY mvnw pom.xml ./
-COPY .mvn .mvn
-COPY src src
-RUN ./mvnw -B package -DskipTests -q
+# Copy root parent POM so Maven can resolve it via relativePath (../pom.xml)
+COPY pom.xml /pom.xml
+COPY backend/mvnw backend/pom.xml ./
+COPY backend/.mvn .mvn
+COPY backend/src src
+RUN --mount=type=cache,target=/root/.m2 ./mvnw -B package -DskipTests -q
 
 # Stage 2: Runtime
 FROM eclipse-temurin:17-jre-alpine

backend/Dockerfile.dockerignore

@@ -0,0 +1,9 @@
+backend/target/
+frontend/
+serverless/
+.git/
+**/.idea/
+**/*.iml
+**/.classpath
+**/.project
+**/.settings/

docker-compose.yml

@@ -1,8 +1,8 @@
 services:
   backend:
     build:
-      context: ./backend
-      dockerfile: Dockerfile
+      context: .
+      dockerfile: backend/Dockerfile
     ports:
       - "8080:8080"
     environment: