feat: 公开商品页重设计 + web 上传修复 + 二维码配置

- 公开商品页（/product/:uuid）全面重设计：全宽正方形图片轮播、
  左右滑动切图、点击放大全屏查看、商品参数含描述、页脚贴底
- 修复 Flutter web 文件上传无反应（path→bytes）
- 修复 web 路由空白页（usePathUrlStrategy + 单层 MaterialApp.router）
- 二维码 URL 改为从 STORAGE_PUBLIC_URL 环境变量读取
- 新增 PUBLIC_URL dart-define → AppConfig.publicBaseUrl
- 新增 CI/CD workflows + NAS runner compose 配置
- seed S001 补充商品描述字段

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

.github/workflows/backup.yml

@@ -0,0 +1,36 @@
+name: DB Backup
+
+on:
+  schedule:
+    - cron: '0 18 * * *'  # UTC 18:00 = 北京时间 02:00
+  workflow_dispatch:
+
+jobs:
+  backup:
+    runs-on: ubuntu-latest
+    steps:
+      - name: Setup SSH
+        run: |
+          mkdir -p ~/.ssh
+          echo "${{ secrets.EC2_SSH_KEY }}" > ~/.ssh/ec2.pem
+          chmod 600 ~/.ssh/ec2.pem
+          ssh-keyscan -H ${{ secrets.EC2_HOST }} >> ~/.ssh/known_hosts
+
+      - name: Dump MySQL to NAS
+        env:
+          EC2_HOST: ${{ secrets.EC2_HOST }}
+          EC2_USER: ${{ secrets.EC2_USER }}
+          DB_PASSWORD: ${{ secrets.DB_PASSWORD }}
+        run: |
+          BACKUP_DIR=/volume1/backups/jiu-db
+          mkdir -p $BACKUP_DIR
+          FILENAME="jiu_db_$(date +%Y%m%d_%H%M%S).sql.gz"
+          ssh -i ~/.ssh/ec2.pem ${EC2_USER}@${EC2_HOST} \
+            "docker exec jiu_mysql mysqldump -uroot -p${DB_PASSWORD} jiu_db" \
+            | gzip > ${BACKUP_DIR}/${FILENAME}
+          find $BACKUP_DIR -name "*.sql.gz" -mtime +30 -delete
+          echo "Saved: ${BACKUP_DIR}/${FILENAME}"
+
+      - name: Cleanup SSH key
+        if: always()
+        run: rm -f ~/.ssh/ec2.pem