fix(scripts): #1894/#1968 抖音 yt-dlp cookies 支持 + 旧档位归一化补测 + CI 覆盖率修复

- scripts_ai.py: 支持通过 DOUYIN_COOKIES_FILE 指定 Netscape cookies 文件；
  cookies 缺失/过期类错误（'fresh cookies' 等）返回 503 + 友好文案
  （'抖音链接解析暂时不可用，请稍后重试或手动输入文案'），
  不再暴露 yt-dlp 原始错误；普通下载失败统一文案，不带内部异常文本
- ci_staging_deploy.sh: API 容器挂载 /var/lib/xiaoxia-saas-staging/configs/douyin_cookies.txt
  到 /app/configs/douyin_cookies.txt；自动 mkdir + 空占位兜底
- infra/docker/compose.yml: API 服务挂载 ../../deploy/configs:/app/configs:ro
- deploy/configs/.env.{staging,production}: 新增 DOUYIN_COOKIES_FILE 环境变量
- deploy/configs/douyin_cookies.txt: Netscape 格式占位文件（真实 cookies 部署时替换）
- 新增 test_helpers_get_user_plan.py 覆盖 _helpers.get_user_plan 旧档位归一化分支
- 新增 test_subscription_routes_legacy.py 覆盖 _build_subscription_info 旧档位归一化/
  cancel_subscription 免费用户分支/change_plan 参数校验/toggle-auto-renew 等
- 扩展 test_extract_from_douyin_errors.py: 新增 5 个 cookies 场景测试（503 友好文案/
  cookiefile 注入/错误信息脱敏等）
- 增量覆盖率从 59% 提升到 60%+，解决 CI Gate 阻塞

scripts/ci_staging_deploy.sh

@@ -47,6 +47,7 @@ ENV_FILE="${ENV_FILE:-/var/lib/xiaoxia-saas-staging/.env}"
 GENERATED_DIR="${GENERATED_DIR:-/var/lib/xiaoxia-saas-staging/generated}"
 LEGACY_ASSETS_DIR="${LEGACY_ASSETS_DIR:-/var/lib/xiaoxia-saas-staging/legacy-assets}"
 NGINX_CONF_FILE="${NGINX_CONF_FILE:-/var/lib/xiaoxia-saas-staging/nginx-staging.conf}"
+COOKIES_FILE="${COOKIES_FILE:-/var/lib/xiaoxia-saas-staging/configs/douyin_cookies.txt}"
 
 SKIP_MIGRATION="${SKIP_MIGRATION:-false}"
 SKIP_ROLLBACK="${SKIP_ROLLBACK:-false}"
@@ -65,6 +66,12 @@ fi
 echo "✅ .env file found: $ENV_FILE ($(wc -l < "$ENV_FILE") lines)"
 mkdir -p "$GENERATED_DIR"
 mkdir -p "$LEGACY_ASSETS_DIR"
+mkdir -p "$(dirname "$COOKIES_FILE")"
+# 确保 cookies 文件存在（即使是空占位），避免容器启动失败
+if [ ! -f "$COOKIES_FILE" ]; then
+  printf '# Netscape HTTP Cookie File\n# 抖音 cookies 文件，如抖音提取功能报 503 请刷新此文件\n' > "$COOKIES_FILE"
+  echo "Created empty cookies placeholder at $COOKIES_FILE"
+fi
 
 # ── 写入 Staging Nginx 配置 ──
 # 运行时覆盖 nginx 配置，确保 upstream 指向正确的 staging 网络
@@ -480,7 +487,9 @@ docker run -d \
   -e GENERATED_FILES_DIR=/app/generated \
   -e GENERATED_FILES_URL_PREFIX=/generated-files \
   -e PUBLIC_API_BASE_URL=https://staging-api.xiaoxiajianji.com \
+  -e DOUYIN_COOKIES_FILE=/app/configs/douyin_cookies.txt \
   -v "$GENERATED_DIR:/app/generated" \
+  -v "$COOKIES_FILE:/app/configs/douyin_cookies.txt:ro" \
   --restart unless-stopped \
   --health-cmd "python -c \"import urllib.request; urllib.request.urlopen('http://localhost:8000/health', timeout=5)\"" \
   --health-interval 30s \