Initial Quartz setup for Castle Docs

quartz/util/lang.ts

@@ -0,0 +1,13 @@
+export function capitalize(s: string): string {
+  return s.substring(0, 1).toUpperCase() + s.substring(1)
+}
+
+export function classNames(
+  displayClass?: "mobile-only" | "desktop-only",
+  ...classes: string[]
+): string {
+  if (displayClass) {
+    classes.push(displayClass)
+  }
+  return classes.join(" ")
+}