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

src/layouts/BaseLayout.astro

@@ -33,7 +33,7 @@ const {
   title,
   description = SITE.description,
   lang = SITE.lang,
-  ogImage = '/og-default.png',
+  ogImage = '/og-default.jpg',
   type = 'website',
   switchHref,
   altLocaleUrl,