ci: 启用BuildKit分布式缓存+Gitea Registry,优化构建速度

- 拆分 requirements.txt: 稳定大包放 requirements-base.txt（numpy/scipy/opencv/Pillow/sqlalchemy 等），业务依赖留 requirements.txt
- 优化 Dockerfile: 分两层安装依赖，基础层缓存命中率高
- CI 改用 docker buildx build，缓存存 Gitea Container Registry
- 启用 Gitea Packages/Container Registry（git.xiaoxiajianji.com）
- 镜像仍推内网 Registry（172.30.18.198:5000），缓存独立存 Gitea Registry

.gitea/workflows/deploy.yml

@@ -64,19 +64,37 @@ jobs:
 
     - name: Build and push staging API/Worker images
       shell: sh
+      env:
+        GITEA_TOKEN: ${{ secrets.GITEA_TOKEN }}
       run: |
         set -eu
         REGISTRY="172.30.18.198:5000"
-        docker build --pull=false \
+        CACHE_REGISTRY="git.xiaoxiajianji.com/xiaoxia/xiaoxia-saas"
+        CACHE_BRANCH="${GITHUB_REF_NAME//\//-}"
+
+        # 登录 Gitea Registry（用于构建缓存）
+        echo "${GITHUB_TOKEN}" | docker login git.xiaoxiajianji.com -u xiaoxia --password-stdin
+
+        # 确保 buildx builder 可用
+        docker buildx use default || docker buildx create --use --name default-builder 2>/dev/null || true
+
+        # 构建 API（带分布式缓存，缓存存 Gitea Registry，镜像推内网 Registry）
+        docker buildx build \
+          --cache-from "type=registry,ref=${CACHE_REGISTRY}/api-cache:${CACHE_BRANCH}" \
+          --cache-to "type=registry,ref=${CACHE_REGISTRY}/api-cache:${CACHE_BRANCH},mode=max" \
           -f infra/docker/api.Dockerfile \
           -t "${REGISTRY}/xiaoxia-saas-api:dev" \
+          --push \
           .
-        docker build --pull=false \
+
+        # 构建 Worker（带分布式缓存）
+        docker buildx build \
+          --cache-from "type=registry,ref=${CACHE_REGISTRY}/worker-cache:${CACHE_BRANCH}" \
+          --cache-to "type=registry,ref=${CACHE_REGISTRY}/worker-cache:${CACHE_BRANCH},mode=max" \
           -f infra/docker/worker.Dockerfile \
           -t "${REGISTRY}/xiaoxia-saas-worker:dev" \
+          --push \
           .
-        docker push "${REGISTRY}/xiaoxia-saas-api:dev"
-        docker push "${REGISTRY}/xiaoxia-saas-worker:dev"
 
     - name: Package staging release artifact
       shell: sh