🐛 fix(api): resolve missing imports in buildApiPayload function

Fix ReferenceError caused by undefined `isValidMessage` and `MESSAGE_ROLES`
in the buildApiPayload function within api.js.

Changes:
- Add missing `isValidMessage` import from utils.js
- Add missing `MESSAGE_ROLES` import from playground constants
- Consolidate duplicate `formatMessageForAPI` import
- Clean up import statements organization

Resolves: ReferenceError: isValidMessage is not defined at buildApiPayload (api.js:39:13)

web/src/helpers/render.js

@@ -1,6 +1,6 @@
 import i18next from 'i18next';
 import { Modal, Tag, Typography } from '@douyinfe/semi-ui';
-import { copy, isMobile, showSuccess } from './index.js';
+import { copy, isMobile, showSuccess } from './utils';
 import { visit } from 'unist-util-visit';
 
 export function renderText(text, limit) {