test(ci): add exporter heading levels and a11y typography smoke; update MAIN_PLAN

tests/e2e/builder-basic.spec.ts

@@ -0,0 +1,7 @@
+import { describe, it, expect } from 'vitest'
+
+describe('e2e placeholder (see .e2e.ts files for Playwright)', () => {
+  it('skips in Vitest environment', () => {
+    expect(true).toBe(true)
+  })
+})