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/DeleteModal.vue

@@ -0,0 +1,53 @@
+<template>
+  <UModal
+    v-model:open="open"
+    :title="`删除 ${item?.name}？`"
+    :description="`确定吗？此操作不可被还原。`"
+  >
+    <slot />
+
+    <template #body>
+      <div class="flex justify-end gap-2">
+        <UButton
+          label="Cancel"
+          color="neutral"
+          variant="subtle"
+          @click="open = false"
+        />
+        <UButton
+          label="Delete"
+          color="error"
+          variant="solid"
+          loading-auto
+          @click="onSubmit"
+        />
+      </div>
+    </template>
+  </UModal>
+</template>
+
+<script lang="ts" setup>
+const props = withDefaults(
+  defineProps<{
+    item?: Item | null;
+  }>(),
+  {
+    item: null,
+  }
+);
+
+const { removeItem } = useItemsStore();
+
+const open = defineModel<boolean>("open", { default: false });
+
+async function onSubmit() {
+  // await new Promise((resolve) => setTimeout(resolve, 1000));
+  if (!props.item || props.item.id == null) {
+    return;
+  }
+  removeItem(props.item.id);
+  open.value = false;
+}
+</script>
+
+<style></style>