chore: 合并为单仓库，统一部署流程

- 根目录加入 docker-compose、Caddyfile、文档等原本不在仓库里的文件
- 前后端两份 GitHub Actions 合并成根目录的一个 deploy workflow：
  构建前端上传到 build/，再在服务器上 git pull 并重建容器

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

api/.github/workflows/depley.yaml

@@ -1,30 +0,0 @@
-name: Deploy
-
-on:
-  push:
-    branches:
-      - main
-
-permissions:
-  contents: read
-
-jobs:
-  deploy:
-    runs-on: ubuntu-latest
-    strategy:
-      fail-fast: false
-      matrix:
-        include:
-          - name: debian
-            remote_port: 22
-          - name: school
-            remote_port: 8822
-    steps:
-      - name: Deploy to ${{ matrix.name }}
-        uses: appleboy/ssh-action@v1
-        with:
-          host: ${{ secrets.HOST }}
-          port: ${{ matrix.remote_port }}
-          username: root
-          key: ${{ secrets.KEY }}
-          script: sh /root/WebPreview/backend.sh