Initial commit: docker-compose-updater

Go 项目，包含：
- 服务端 updater：两阶段协议，ECDSA 签名验证，AES-GCM 加密
- 发送端 dcu-send：Gitea Action CLI
- internal/auth：加解密/签名/会话管理
- internal/docker：Docker CLI 容器查找/拉取/重建
- action/：Gitea Action 定义
- deploy/Dockerfile：多阶段构建
- .gitea/workflows/build.yaml：CI/CD

.gitea/workflows/build.yaml

@@ -0,0 +1,28 @@
+name: Build and Push
+on:
+  push:
+    branches: [main]
+
+jobs:
+  build:
+    runs-on: ubuntu-latest
+    steps:
+      - uses: actions/checkout@v4
+
+      - name: Build updater binary (test only)
+        run: |
+          go mod download
+          go build -o /dev/null ./cmd/updater
+          go build -o /dev/null ./cmd/dcu-send
+
+      - name: Log in to registry
+        run: docker login -u ${{ secrets.REGISTRY_USER }} -p ${{ secrets.REGISTRY_PASS }} ${{ secrets.REGISTRY_URL }}
+
+      - name: Build and push updater image
+        run: |
+          PUBLIC_KEY_BASE64=$(base64 -w0 < keys/signing-public.pem)
+          docker build \
+            --build-arg PUBLIC_KEY_BASE64=$PUBLIC_KEY_BASE64 \
+            -t ${{ secrets.REGISTRY_URL }}/docker-compose-updater:latest \
+            -f deploy/Dockerfile .
+          docker push ${{ secrets.REGISTRY_URL }}/docker-compose-updater:latest