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

lib/exporter/a11yResponsive.test.ts

@@ -41,7 +41,7 @@ describe('Exporter a11y/responsive enhancements', () => {
   test('hero image alt derives from heading', () => {
     const out = exportPage(makePage())
     expect(out.html).toContain('<h1 id="hero-heading">Welcome</h1>')
-    expect(out.html).toContain('<img src="https://example.com/img.png" alt="Welcome" />')
+    expect(out.html).toMatch(/<img[^>]*src="https:\/\/example\.com\/img\.png"[^>]*alt="Welcome"[^>]*\/>/)
   })
 
   test('responsive and a11y CSS tokens exist', () => {

lib/exporter/html.ts

@@ -108,7 +108,7 @@ function renderHero(section: { props: { heading: string; subheading?: string; im
           ${subheading ? `<p>${escapeHtml(subheading)}</p>` : ''}
         </div>
         <div class="media">
-          <img src="${escapeHtml(imageUrl)}" alt="${escapeHtml(heading)}" />
+          <img src="${escapeHtml(imageUrl)}" alt="${escapeHtml(heading)}" loading="lazy" decoding="async" />
         </div>
       </div>
     </section>
@@ -237,6 +237,7 @@ function buildHead(page: Page) {
   return `
     <meta charset="utf-8" />
     <meta name="viewport" content="width=device-width, initial-scale=1" />
+    <link rel="canonical" href="/" />
     <title>${escapeHtml(page.seo.title)}</title>
     <meta name="description" content="${escapeHtml(page.seo.description)}" />
     <meta property="og:title" content="${escapeHtml(page.seo.title)}" />
@@ -272,6 +273,7 @@ function buildCss(page: Page) {
   .testimonial blockquote{ margin:0; font-style:italic; color:#1f2937 }
   .testimonial figcaption{ color:#475569; margin-top:.25rem }
   @media (max-width: 640px){ .container{ padding: 1rem } h1{ font-size: 1.5rem } }
+  @media (prefers-color-scheme: dark){ body{ color:#e5e7eb; background:#0b1020 } .feature-item{ background:#0f172a; border-color:#1f2937 } }
   @media (prefers-reduced-motion: reduce){ *{ transition: none !important; animation: none !important } }
   `
 }

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 \(prefers-color-scheme: dark\)/)
+  })
+})