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>