feat(design): deploy default OG card (JPG/PNG), complete banner hygiene (E8), modernize CJK typography (E9), align title & hero (A2)

src/pages/posts/[...slug].astro

@@ -62,7 +62,7 @@ const jsonLd = {
   mainEntityOfPage: { '@type': 'WebPage', '@id': postUrl },
   headline: post.data.title,
   description: post.data.description,
-  image: new URL(post.data.ogImage ?? '/og-default.png', SITE.url).href,
+  image: new URL(post.data.ogImage ?? '/og-default.jpg', SITE.url).href,
   inLanguage: lang === 'zh' ? 'zh' : 'en',
   datePublished: post.data.pubDate.toISOString(),
   dateModified: (post.data.updatedDate ?? post.data.pubDate).toISOString(),
@@ -79,7 +79,7 @@ const jsonLd = {
   title={`${post.data.title} — Mr Hoelee`}
   description={post.data.description}
   lang={lang}
-  ogImage={post.data.ogImage ?? '/og-default.png'}
+  ogImage={post.data.ogImage ?? '/og-default.jpg'}
   type="article"
   switchHref={switchHref}
   altLocaleUrl={altLocaleUrl}