fix(baoyu-post-to-x): add missing fs import in x-article

skills/baoyu-post-to-x/scripts/x-article.ts

@@ -1,3 +1,4 @@
+import fs from 'node:fs';
 import { mkdir, writeFile } from 'node:fs/promises';
 import os from 'node:os';
 import path from 'node:path';