feat: 이미지 최적화 옵션 추가(fetchpriority/srcset/sizes) (TDD)

- ExportOptions에 이미지 옵션 추가
- hero 이미지에 조건부 속성 렌더링
- 테스트: image.responsive.options.test.ts
- 전체 테스트 그린 유지

lib/exporter/html.ts

@@ -9,6 +9,9 @@ export type ExportOptions = {
   robotsMeta?: string
   imageLoading?: 'lazy' | 'eager'
   imageDecoding?: 'async' | 'sync'
+  imageFetchPriority?: 'high' | 'low'
+  imageSrcset?: string
+  imageSizes?: string
 }
 
 function renderFaq(section: { props: { items: Array<{ q: string; a: string }> } }) {
@@ -125,6 +128,9 @@ function renderHero(section: { props: { heading: string; subheading?: string; im
   const imageUrl = am ? am.rewriteUrl(imageUrlRaw) : imageUrlRaw
   const loading = opts?.imageLoading ?? 'lazy'
   const decoding = opts?.imageDecoding ?? 'async'
+  const fetchpriority = opts?.imageFetchPriority ? ` fetchpriority="${escapeHtml(opts.imageFetchPriority)}"` : ''
+  const srcset = opts?.imageSrcset ? ` srcset="${escapeHtml(opts.imageSrcset)}"` : ''
+  const sizes = opts?.imageSizes ? ` sizes="${escapeHtml(opts.imageSizes)}"` : ''
   return `
     <section class="hero" aria-labelledby="hero-heading">
       <div class="container">
@@ -133,7 +139,7 @@ function renderHero(section: { props: { heading: string; subheading?: string; im
           ${subheading.length > 0 ? `<p>${escapeHtml(subheading)}</p>` : ''}
         </div>
         <div class="media">
-          <img src="${escapeHtml(imageUrl)}" alt="${escapeHtml(heading)}" loading="${escapeHtml(loading)}" decoding="${escapeHtml(decoding)}" width="1200" height="675" />
+          <img src="${escapeHtml(imageUrl)}" alt="${escapeHtml(heading)}" loading="${escapeHtml(loading)}" decoding="${escapeHtml(decoding)}"${fetchpriority}${srcset}${sizes} width="1200" height="675" />
         </div>
       </div>
     </section>

lib/exporter/image.responsive.options.test.ts

@@ -0,0 +1,38 @@
+import { describe, it, expect } from 'vitest'
+import { exportPage } from '@/lib/exporter/html'
+import type { ExportOptions } from '@/lib/exporter/html'
+import type { Page } from '@/lib/schema/page'
+
+const basePage: Page = {
+  title: 'Img Test',
+  locale: 'en',
+  theme: { primaryColor: '#0ea5e9', fontFamily: 'Inter' },
+  sections: [
+    { type: 'hero', props: { heading: 'Hero', subheading: '', imageUrl: 'https://example.com/hero.jpg' } },
+  ],
+  form: {
+    actionUrl: '',
+    fields: [],
+    spamProtection: { honeypotFieldName: '_hp', minSubmitSeconds: 2 },
+  },
+  analytics: { ga4MeasurementId: '', metaPixelId: '', customHeadHtml: '' },
+  seo: { title: 'T', description: 'D' },
+}
+
+describe('image responsive/export options', () => {
+  it('applies fetchpriority when provided', () => {
+    const options: ExportOptions = { imageLoading: 'eager', imageDecoding: 'async', imageFetchPriority: 'high' }
+    const { html } = exportPage(basePage, options)
+    expect(html).toMatch(/<img[^>]*fetchpriority="high"/)
+  })
+
+  it('applies srcset and sizes when provided', () => {
+    const options: ExportOptions = {
+      imageSrcset: 'https://example.com/hero.jpg 1x, https://example.com/hero@2x.jpg 2x',
+      imageSizes: '(max-width: 640px) 100vw, 600px',
+    }
+    const { html } = exportPage(basePage, options)
+    expect(html).toMatch(/<img[^>]*srcset="https:\/\/example.com\/hero.jpg 1x, https:\/\/example.com\/hero@2x.jpg 2x"/)
+    expect(html).toMatch(/<img[^>]*sizes="\(max-width: 640px\) 100vw, 600px"/)
+  })
+})