默认极速模式（qwen-flash，首字秒回+内置知识库）；百炼智能体模式走应用编排（知识库 RAG，回答更全但更慢）。Key 仅保存在本机浏览器。对外分发前请改走网关。 Default fast mode (qwen-flash, instant first token + built-in KB); Agent mode uses Bailian orchestration (RAG, more thorough but slower). Keys are stored only in this browser. Route via gateway before public distribution.