feat: use nuxt 4 structure

app/composables/count.ts

@@ -0,0 +1,16 @@
+export function useCount() {
+  const count = useState('count', () => Math.round(Math.random() * 20))
+
+  function inc() {
+    count.value += 1
+  }
+  function dec() {
+    count.value -= 1
+  }
+
+  return {
+    count,
+    inc,
+    dec,
+  }
+}