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/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"/)
+  })
+})