refactor(insta): instaUtils(fmtDate)+usePollTask 훅+StatusBadge/TaskStatusBox 추출

src/pages/insta/instaUtils.test.js

@@ -0,0 +1,15 @@
+import { describe, it, expect } from 'vitest';
+import { fmtDate } from './instaUtils';
+
+describe('instaUtils.fmtDate', () => {
+  it('returns empty string for falsy input', () => {
+    expect(fmtDate('')).toBe('');
+    expect(fmtDate(null)).toBe('');
+    expect(fmtDate(undefined)).toBe('');
+  });
+  it('returns a non-empty string for a valid ISO date (locale/tz-dependent format)', () => {
+    const out = fmtDate('2026-07-10T09:30:00Z');
+    expect(typeof out).toBe('string');
+    expect(out.length).toBeGreaterThan(0);
+  });
+});