feat(ui): implement dashboard layout and refactor pages

This commit replaces the previous simple layout with a comprehensive dashboard interface using Nuxt UI Pro components.

- Introduced a new default layout with `UDashboardSidebar` and `UDashboardPanel`.
- Refactored the main page (`index.vue`) by splitting it into `ItemManageStatistics` and `ItemManageTable` components.
- Added new computed stats for monthly growth and total images, and displayed them in new statistic cards.
- Reorganized components from `item/` to a new `itemManage/` directory.
- Added custom primary and secondary theme colors.

app/components/itemManage/Statistics.vue

@@ -0,0 +1,76 @@
+<template>
+  <!-- 统计 -->
+  <div class="grid grid-cols-1 md:grid-cols-4 gap-6 mb-8">
+    <UCard v-for="stat in statistics" :key="stat.label">
+      <div class="space-y-2">
+        <div class="flex items-center justify-between">
+          <p class="text-sm text-gray-500 dark:text-gray-400">
+            {{ stat.label }}
+          </p>
+          <UIcon
+            :name="stat.icon"
+            :style="`color: ${stat.color}`"
+            class="size-5 text-gray-400"
+          />
+        </div>
+        <p class="text-3xl font-bold">{{ stat.value }}</p>
+        <div v-if="stat.percentage" class="flex items-center gap-1 text-sm">
+          <UIcon
+            :name="stat.percentageIcon"
+            :class="['size-4', stat.percentageColor]"
+          />
+          <span :class="['font-medium', stat.percentageColor]">{{
+            stat.percentageChange
+          }}</span>
+          <span class="text-gray-500">{{ stat.percentageLabel }}</span>
+        </div>
+      </div>
+    </UCard>
+  </div>
+</template>
+
+<script lang="ts" setup>
+const { stats } = useItemsStore();
+
+// 统计
+const statistics = [
+  {
+    icon: "lucide:box",
+    label: "总物品数",
+    value: stats.totalItems,
+    color: "blue",
+  },
+  {
+    icon: "lucide:package-plus",
+    label: "本月新增",
+    value: stats.addedThisMonth,
+    color: "green",
+    percentage: true,
+    percentageChange:
+      stats.comparedToLastMonth.value >= 0
+        ? `+${stats.comparedToLastMonth.value}%`
+        : `${stats.comparedToLastMonth.value}%`,
+    percentageLabel: "from last month",
+    percentageIcon:
+      stats.comparedToLastMonth.value >= 0
+        ? "i-lucide-trending-up"
+        : "i-lucide-trending-down",
+    percentageColor:
+      stats.comparedToLastMonth.value >= 0 ? "text-green-500" : "text-red-500",
+  },
+  {
+    icon: "lucide:history",
+    label: "历史记录",
+    value: computed(() => 0),
+    color: "orange",
+  },
+  {
+    icon: "lucide:image",
+    label: "图片总数",
+    value: stats.totalImages,
+    color: "purple",
+  },
+];
+</script>
+
+<style></style>