Composition API と Options API の違いは何ですか？

<script>
export default {
  data() { return { count: 0 }; },
  computed: { double() { return this.count * 2; } },
  methods: { increment() { this.count++; } },
  mounted() { console.log("mounted"); },
};
</script>

<script setup>
import { ref, computed, onMounted } from "vue";

// all the logic for "counter" lives together
const count = ref(0);
const double = computed(() => count.value * 2);
function increment() { count.value++; }
onMounted(() => console.log("mounted"));
</script>

// useCounter.js — reusable across any component
export function useCounter() {
  const count = ref(0);
  const increment = () => count.value++;
  return { count, increment };
}

<script setup>
const { count, increment } = useCounter(); // reuse anywhere
</script>

Options API     → simpler mental model, fine for small components, familiar to beginners
Composition API → better for large components, TypeScript, and reusing logic (composables)