refactor: organize desktop vs. mobile into separate folders

js/desktop/src/lib/keyboard.ts

@@ -0,0 +1,9 @@
+export function isTypingTarget(e: KeyboardEvent): boolean {
+  const target = e.target as HTMLElement | null;
+  if (!target) return false;
+  return (
+    target.tagName === "INPUT" ||
+    target.tagName === "TEXTAREA" ||
+    target.isContentEditable
+  );
+}