feat(exporter): SEO/Perf small improvements (canonical, lazy/async hero, dark token) + tests

lib/exporter/seoPerf.tokens.test.ts

@@ -0,0 +1,34 @@
+import { describe, it, expect } from 'vitest'
+import { exportPage } from '@/lib/exporter/html'
+import { pageSchema, type Page } from '@/lib/schema/page'
+
+function makePage(): Page {
+  return pageSchema.parse({
+    title: 'SEO/Perf',
+    locale: 'en',
+    theme: { primaryColor: '#0ea5e9', fontFamily: 'Inter' },
+    sections: [
+      { type: 'hero', props: { heading: 'Welcome', subheading: 'Sub', imageUrl: 'https://img.example/hero.png' } },
+    ],
+    form: { actionUrl: '', fields: [], spamProtection: { honeypotFieldName: '_hp', minSubmitSeconds: 2 } },
+    seo: { title: 'SEO', description: 'Desc' },
+  })
+}
+
+describe('Exporter - small SEO/Perf improvements', () => {
+  it('includes canonical link and dark mode tokens; hero image lazy/async', () => {
+    const out = exportPage(makePage())
+    const html = out.html
+    const css = out.css
+
+    // canonical link present in head
+    expect(html).toMatch(/<link[^>]+rel="canonical"/)
+
+    // hero image has loading/decoding attributes
+    expect(html).toMatch(/<img[^>]*loading="lazy"/)
+    expect(html).toMatch(/<img[^>]*decoding="async"/)
+
+    // dark mode media query token exists
+    expect(css).toMatch(/@media \(prefers-color-scheme: dark\)/)
+  })
+})