feat: PostItem 스토리북 추가

src/stories/components/PostItem.stories.tsx

@@ -0,0 +1,20 @@
+import type { Meta, StoryObj } from '@storybook/react';
+
+import PostItem from '@/src/app/main/_component/PostItem';
+
+const meta: Meta<typeof PostItem> = {
+  title: 'components/PostItem',
+  tags: ['autodocs'],
+  component: PostItem,
+};
+
+export default meta;
+
+type Story = StoryObj<typeof PostItem>;
+
+export const DefaultTemplate: Story = {
+  args: {
+    size: 20,
+    id: 'add',
+  },
+};