refactor: 使用 openai SDK 替换 fetch 调用 LLM

- 安装 openai 包
- 重命名 zhipu.ts -> llm.ts
- 使用 OpenAI SDK 替代原生 fetch 实现
- 更新所有导入路径

src/modules/translator/translator-action.ts

@@ -8,7 +8,7 @@ import {
 import { ValidateError } from "@/lib/errors";
 import { createLogger } from "@/lib/logger";
 import { serviceTranslateText } from "./translator-service";
-import { getAnswer } from "@/lib/bigmodel/zhipu";
+import { getAnswer } from "@/lib/bigmodel/llm";
 
 const log = createLogger("translator-action");