feat(items): implement initial item management system

This commit introduces the foundational structure and core features for the item management application.

Key features implemented:
- **Item Listing:** A main page displaying all items in a searchable UTable.
- **Item Creation:** An "Add Item" modal with a UForm for input and validation using Zod.
- **State Management:** A `useItemsStore` composable built with `@vueuse/core`'s `useLocalStorage` to persist item data
in the browser.
- **UI Framework:** Integrated Nuxt UI for components like tables, modals, forms, and the overall layout.
- **Application Shell:** Established a default layout with a header, navigation menu, and placeholders for Export and
History pages.
- **Project Setup:** Configured pnpm workspace, Tailwind CSS, and VSCode editor settings for an improved development
experience.

app/layouts/default.vue

@@ -0,0 +1,54 @@
+<template>
+  <div>
+    <!-- 导航栏 -->
+    <UHeader>
+      <template #title>物品数据库</template>
+
+      <UNavigationMenu :items="items" />
+
+      <template #right>
+        <UColorModeButton />
+
+        <UTooltip text="Open on GitHub" :kbds="['meta', 'G']">
+          <UButton
+            color="neutral"
+            variant="ghost"
+            to="https://github.com/nuxt/ui"
+            target="_blank"
+            icon="i-simple-icons-github"
+            aria-label="GitHub"
+          />
+        </UTooltip>
+      </template>
+    </UHeader>
+
+    <!-- 页面内容插槽 -->
+    <slot />
+  </div>
+</template>
+
+<script setup lang="ts">
+import type { NavigationMenuItem } from "@nuxt/ui";
+
+const route = useRoute();
+
+const items = computed<NavigationMenuItem[]>(() => [
+  {
+    label: "物品管理",
+    to: "/",
+    icon: "marketeq:home-alt-3",
+  },
+  {
+    label: "导出配置",
+    to: "/export",
+    active: route.path.startsWith("/export"),
+    icon: "marketeq:export-2",
+  },
+  {
+    label: "历史记录",
+    to: "/history",
+    active: route.path.startsWith("/history"),
+    icon: "marketeq:chart-line-alt-1",
+  },
+]);
+</script>