feat: enhance user experience with custom 404 page, breadcrumbs, and mobile ToC; add callout styles and language labels

languages/en.json

@@ -18,6 +18,11 @@
 	"Copy link": "Copy link",
 	"Link copied": "Link copied",
 	"Related posts": "Related posts",
+	"Home": "Home",
+	"On this page": "On this page",
+	"Page not found": "Page not found",
+	"The page you are looking for does not exist or has moved.": "The page you are looking for does not exist or has moved.",
+	"Back to home": "Back to home",
 	"Previous": "Previous",
 	"Next": "Next",
 	"Updated": "Updated",