refactor(agent): 修改环境变量名并优化代码格式

- 将环境变量名从 BAILIAN_CLI_API_KEY 改为 DASHSCOPE_API_KEY
- 调整导入语句格式，提升代码可读性
- 优化 providers 条目查找的换行和缩进
- 标准化名称判断与赋值逻辑的格式与排列

Author: lishengzxc

packages/commands/src/commands/config/agent/writers/qwen-code.ts

@@ -2,7 +2,7 @@ import { homedir } from "os";
 import { join } from "path";
 import { backup, readJson, writeJsonAtomic, isAnthropicEndpoint, type AgentDef } from "./utils.ts";
 
-const ENV_KEY = "BAILIAN_CLI_API_KEY";
+const ENV_KEY = "DASHSCOPE_API_KEY";
 
 function displayName(model: string): string {
   return `[Bailian] ${model}`;