feat(theme): extend titleTemplate by replacing the title (#1200)

src/shared/shared.ts

@@ -104,6 +104,11 @@ export function resolveSiteDataByRoute(
 export function createTitle(siteData: SiteData, pageData: PageData): string {
   const title = pageData.title || siteData.title
   const template = pageData.titleTemplate ?? siteData.titleTemplate
+
+  if (typeof template === 'string' && template.includes(':title')) {
+    return template.replace(/:title/g, title)
+  }
+
   const templateString = createTitleTemplate(siteData.title, template)
 
   return `${title}${templateString}`