部署迁移：VPS 本机构建 → GitHub Actions 构建镜像推送 ghcr.io

CI 新增 build-and-push job，测试通过后构建 backend/frontend 镜像推送 ghcr.io。
VPS 部署改为 docker compose pull + up -d，不再本地编译。

.github/workflows/ci.yml

@@ -54,10 +54,56 @@ jobs:
       - name: Build
         run: npm run build
 
-  deploy:
+  build-and-push:
     needs: [python-quality, frontend-quality]
     if: github.event_name == 'push' && github.ref == 'refs/heads/main'
     runs-on: ubuntu-latest
+    permissions:
+      contents: read
+      packages: write
+    steps:
+      - name: Checkout
+        uses: actions/checkout@v4
+
+      - name: Login to GHCR
+        uses: docker/login-action@v3
+        with:
+          registry: ghcr.io
+          username: ${{ github.actor }}
+          password: ${{ secrets.GITHUB_TOKEN }}
+
+      - name: Build and push backend image
+        uses: docker/build-push-action@v6
+        with:
+          context: .
+          push: true
+          tags: |
+            ghcr.io/yangyuan-zhen/polyweather-backend:latest
+            ghcr.io/yangyuan-zhen/polyweather-backend:${{ github.sha }}
+          cache-from: type=gha
+          cache-to: type=gha,mode=max
+
+      - name: Build and push frontend image
+        uses: docker/build-push-action@v6
+        with:
+          context: ./frontend
+          push: true
+          tags: |
+            ghcr.io/yangyuan-zhen/polyweather-frontend:latest
+            ghcr.io/yangyuan-zhen/polyweather-frontend:${{ github.sha }}
+          build-args: |
+            NEXT_PUBLIC_SUPABASE_URL=${{ secrets.NEXT_PUBLIC_SUPABASE_URL }}
+            NEXT_PUBLIC_SUPABASE_ANON_KEY=${{ secrets.NEXT_PUBLIC_SUPABASE_ANON_KEY }}
+            NEXT_PUBLIC_SITE_URL=${{ secrets.NEXT_PUBLIC_SITE_URL || 'https://polyweather.top' }}
+            NEXT_PUBLIC_POLYWEATHER_API_BASE_URL=${{ secrets.NEXT_PUBLIC_POLYWEATHER_API_BASE_URL || 'https://api.polyweather.top' }}
+            NEXT_PUBLIC_POLYWEATHER_LOCAL_FULL_ACCESS=false
+          cache-from: type=gha
+          cache-to: type=gha,mode=max
+
+  deploy:
+    needs: [build-and-push]
+    if: github.event_name == 'push' && github.ref == 'refs/heads/main'
+    runs-on: ubuntu-latest
     steps:
       - name: Deploy to VPS
         run: |
@@ -65,10 +111,11 @@ jobs:
           echo "${{ secrets.VPS_SSH_KEY }}" > ~/.ssh/id_rsa
           chmod 600 ~/.ssh/id_rsa
           ssh -o StrictHostKeyChecking=accept-new ${{ secrets.VPS_USER }}@${{ secrets.VPS_HOST }} "
+            echo '${{ secrets.GHCR_PAT }}' | docker login ghcr.io -u yangyuan-zhen --password-stdin
             cd /root/PolyWeather
             git fetch origin main && git reset --hard origin/main
-            docker compose down
-            docker compose up -d --build
+            docker compose pull
+            docker compose up -d
             sleep 10
             curl -s http://localhost:8000/healthz
           "