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/composables/items.ts

@@ -61,6 +61,45 @@ const _useItems = () => {
           item.createdAt?.getFullYear() === thisYear
       ).length;
     }),
+    // Compared to last month
+    comparedToLastMonth: computed(() => {
+      const now = new Date();
+      const thisMonth = now.getMonth();
+      const thisYear = now.getFullYear();
+
+      const lastMonthDate = new Date(now);
+      lastMonthDate.setMonth(thisMonth - 1);
+      const lastMonth = lastMonthDate.getMonth();
+      const lastMonthYear = lastMonthDate.getFullYear();
+
+      const thisMonthCount = (items.value ?? []).filter(
+        (item) =>
+          item.createdAt?.getMonth() === thisMonth &&
+          item.createdAt?.getFullYear() === thisYear
+      ).length;
+
+      const lastMonthCount = (items.value ?? []).filter(
+        (item) =>
+          item.createdAt?.getMonth() === lastMonth &&
+          item.createdAt?.getFullYear() === lastMonthYear
+      ).length;
+
+      // if (lastMonthCount === 0) {
+      //   return thisMonthCount === 0 ? 0 : 100;
+      // }
+
+      // return ((thisMonthCount - lastMonthCount) / lastMonthCount) * 100;
+      if (lastMonthCount === 0) {
+        // 上个月为 0，本月不为 0 → 直接视为无限增长（返回 100 * thisMonthCount）
+        return thisMonthCount === 0 ? 0 : thisMonthCount * 100;
+      }
+
+      // 允许超过 100% 的差值百分比
+      return ((thisMonthCount - lastMonthCount) / lastMonthCount) * 100;
+    }),
+    totalImages: computed(() => {
+      return (items.value ?? []).filter((item) => item.imageUrl).length;
+    }),
   };
 
   const utils = {