[game] Walk controls (unbound)

src/input.ts

@@ -0,0 +1,11 @@
+export const Button = {
+  Up: 0,
+  Down: 1,
+  Left: 2,
+  Right: 3,
+} as const;
+type Button = (typeof Button)[keyof typeof Button];
+
+export function btn(_which: Button): boolean {
+  return false;
+}