fix: add DATABASE_URL export for backend database connection

spug/deploy-docker-compose.sh

@@ -23,6 +23,9 @@ export DATABASE_NAME="${DATABASE_NAME:-hospital_performance}"
 export SECRET_KEY="${SECRET_KEY:-change-this-secret-key-in-production}"
 export DEBUG="${DEBUG:-False}"
 
+# 构建完整的 DATABASE_URL（后端使用此变量）
+export DATABASE_URL="postgresql+asyncpg://${DATABASE_USER}:${DATABASE_PASSWORD}@${DATABASE_HOST}:${DATABASE_PORT}/${DATABASE_NAME}"
+
 # 日志配置
 LOG_FILE="/tmp/spug-deploy-$(date +%Y%m%d_%H%M%S).log"