fix(docker): surface backend crash logs in docker logs and print DB target

docker/start-backend.sh

@@ -0,0 +1,22 @@
+#!/bin/sh
+set -eu
+
+cd /app
+
+echo "[backend-wrapper] starting taskpool server"
+echo "[backend-wrapper] cwd=$(pwd)"
+echo "[backend-wrapper] BH_SERVER_HOST=${BH_SERVER_HOST:-}"
+echo "[backend-wrapper] BH_SERVER_PORT=${BH_SERVER_PORT:-}"
+echo "[backend-wrapper] BH_DB_TYPE=${BH_DB_TYPE:-}"
+echo "[backend-wrapper] BH_DB_HOST=${BH_DB_HOST:-}"
+echo "[backend-wrapper] BH_DB_PORT=${BH_DB_PORT:-}"
+echo "[backend-wrapper] BH_DB_USER=${BH_DB_USER:-}"
+echo "[backend-wrapper] BH_DB_NAME=${BH_DB_NAME:-}"
+echo "[backend-wrapper] BH_DB_PATH=${BH_DB_PATH:-}"
+echo "[backend-wrapper] config.ini exists=$([ -f /app/configs/config.ini ] && echo yes || echo no)"
+
+# 避免空目录挂载导致权限/路径问题
+mkdir -p /app/data /app/configs /app/envs /app/logs /app/data/scripts
+
+# 直接前台运行，日志打到容器 stdout/stderr，方便 docker logs 排查
+exec /app/taskpool server