feat(export): implement export page for bidding items

Introduces a new export page for creating and managing bidding lists. Key features include: selecting items from a
master list, adding them to a bidding list, editing start price/remarks, batch price updates, and drag-and-drop
reordering. The final list can be previewed and exported as a CSV. This change adds the `useBiddingItems` composable and
the `sortablejs` dependency. Also refactors `imageUrl` to be a non-nullable string for type consistency.

app/components/export/EditModal.vue

@@ -0,0 +1,79 @@
+<template>
+  <UModal v-model:open="open" title="编辑标品">
+    <template #body>
+      <UForm
+        @submit="onSubmit"
+        :state="biddingItemEditState"
+        :schema="biddingItemEditSchema"
+      >
+        <UFormField label="起拍价" name="startPrice">
+          <UInput
+            v-model.number="biddingItemEditState.startPrice"
+            type="number"
+          />
+        </UFormField>
+
+        <UFormField label="备注" name="remarks">
+          <UTextarea v-model="biddingItemEditState.remarks" />
+        </UFormField>
+
+        <UButton type="submit" label="保存" color="primary" class="mt-4" />
+      </UForm>
+    </template>
+  </UModal>
+</template>
+
+<script lang="ts" setup>
+import type { FormSubmitEvent } from "@nuxt/ui";
+import * as z from "zod";
+
+const biddingItemEditForm = ref();
+const currentId = ref<number>(0);
+const open = ref<boolean>(false);
+
+const toast = useToast();
+
+const { biddingItems, editBiddingItem } = useBiddingItems();
+
+const biddingItemEditSchema = z.object({
+  startPrice: z.number().min(0, "起拍价不能少于 RM 0").default(0),
+  remarks: z.string().optional(),
+});
+
+type BiddingItemEditSchema = z.output<typeof biddingItemEditSchema>;
+
+const biddingItemEditState = reactive<BiddingItem & BiddingItemEditSchema>({
+  id: 0,
+  name: "",
+  imageUrl: "",
+  startPrice: 0,
+  remarks: "",
+});
+
+const openModal = (biddingItem: BiddingItem) => {
+  Object.assign(biddingItemEditState, biddingItem); // 👈 一次性复制所有字段
+  currentId.value = biddingItem.id;
+  open.value = true;
+};
+
+const onSubmit = async (event: FormSubmitEvent<BiddingItemEditSchema>) => {
+  const updatedItem: BiddingItem = {
+    ...biddingItemEditState, // 👈 这里直接复用已有字段
+    startPrice: event.data.startPrice,
+    remarks: event.data.remarks ?? "",
+  };
+
+  editBiddingItem(updatedItem);
+  toast.add({
+    title: "已保存修改",
+    description: `${updatedItem.name} 的信息已更新`,
+    color: "success",
+  });
+
+  open.value = false;
+};
+
+defineExpose({ openModal });
+</script>
+
+<style></style>

app/components/item/EditModal.vue

@@ -100,7 +100,7 @@ const { utils, isNameAvailable, addItem, editItem, items } = useItemsStore();
 const baseSchema = z.object({
   brand: z.string().optional(),
   name: z.string().min(1, "名称不能为空"),
-  imageUrl: z.string().nullable().optional(),
+  imageUrl: z.string().optional(),
   description: z.string().nullable().optional(),
   tags: z.string().nullable().optional(),
 });
@@ -121,7 +121,7 @@ type ItemSchema = z.output<typeof baseSchema>;
 const itemState = reactive<ItemSchema>({
   brand: undefined,
   name: "",
-  imageUrl: null,
+  imageUrl: "",
   description: null,
   tags: null,
 });
@@ -134,7 +134,7 @@ const openModal = (item?: Item) => {
     currentId.value = item.id;
     itemState.brand = item.brand;
     itemState.name = item.name;
-    itemState.imageUrl = item.imageUrl ?? null;
+    itemState.imageUrl = item.imageUrl;
     itemState.description = item.description ?? null;
     itemState.tags = item.tags?.join(", ") ?? null;
   } else {
@@ -143,7 +143,7 @@ const openModal = (item?: Item) => {
     itemState.brand = undefined;
     currentId.value = null;
     itemState.name = "";
-    itemState.imageUrl = null;
+    itemState.imageUrl = "";
     itemState.description = null;
     itemState.tags = null;
   }