feat: 重构后台路由并使用嵌套路由；添加图片上传功能

- 拆分 AdminView 为多个子页面组件，使用嵌套路由
- 拆分 MerchantView 为多个子页面组件，使用嵌套路由
- 创建 AdminLayout 和 MerchantLayout 布局组件
- 修复编译错误：IconSend 重复导入、IconDatabase 不存在
- 修复 HomeView 缺失 onMounted 导入
- 添加文件上传后端接口和静态资源映射
- 为商品和轮播图添加图片上传功能（支持预览、清除）

frontend/src/views/merchant/MerchantLayout.vue

@@ -0,0 +1,126 @@
+<template>
+  <a-layout style="min-height: 100vh" class="merchant-layout">
+    <a-layout-sider :width="240" theme="dark" collapsible v-model:collapsed="collapsed" :collapsed-width="64" class="merchant-sider">
+      <div class="sider-header">
+        <a-avatar :size="36" style="background: linear-gradient(135deg, #52c41a 0%, #73d13d 100%)">
+          <icon-home />
+        </a-avatar>
+        <span class="sider-title" v-if="!collapsed">商家后台</span>
+      </div>
+      <a-menu :selected-keys="[$route.name]" @menu-item-click="onMenuClick" theme="dark">
+        <a-menu-item key="merchant-overview">
+          <template #icon><icon-dashboard /></template>
+          <span v-if="!collapsed">数据概览</span>
+        </a-menu-item>
+        <a-menu-item key="merchant-products">
+          <template #icon><icon-apps /></template>
+          <span v-if="!collapsed">商品管理</span>
+        </a-menu-item>
+        <a-menu-item key="merchant-orders">
+          <template #icon><icon-file /></template>
+          <span v-if="!collapsed">订单管理</span>
+        </a-menu-item>
+        <a-menu-item key="merchant-reviews">
+          <template #icon><icon-message /></template>
+          <span v-if="!collapsed">评价管理</span>
+        </a-menu-item>
+        <a-menu-item key="merchant-logistics">
+          <template #icon><icon-send /></template>
+          <span v-if="!collapsed">物流管理</span>
+        </a-menu-item>
+        <a-menu-item key="merchant-inventory">
+          <template #icon><icon-storage /></template>
+          <span v-if="!collapsed">库存管理</span>
+        </a-menu-item>
+        <a-menu-item key="merchant-profile">
+          <template #icon><icon-user /></template>
+          <span v-if="!collapsed">个人信息</span>
+        </a-menu-item>
+      </a-menu>
+    </a-layout-sider>
+    <a-layout class="merchant-main">
+      <a-layout-header class="merchant-header">
+        <div class="header-left">
+          <span class="page-title">{{ titleMap[$route.name] || '商家后台' }}</span>
+        </div>
+        <div class="header-right">
+          <a-space>
+            <a-button @click="goHome">
+              <template #icon><icon-home /></template>
+              去商城
+            </a-button>
+            <a-dropdown>
+              <a-button shape="circle">
+                <template #icon><icon-user /></template>
+              </a-button>
+              <template #content>
+                <a-doption @click="goProfile">
+                  <template #icon><icon-settings /></template>
+                  个人信息
+                </a-doption>
+                <a-doption @click="logout">
+                  <template #icon><icon-export /></template>
+                  退出登录
+                </a-doption>
+              </template>
+            </a-dropdown>
+          </a-space>
+        </div>
+      </a-layout-header>
+      <a-layout-content class="merchant-content">
+        <router-view />
+      </a-layout-content>
+    </a-layout>
+  </a-layout>
+</template>
+
+<script setup>
+import { ref, onMounted } from 'vue'
+import { useRouter, useRoute } from 'vue-router'
+import { useUserStore } from '../../stores/user'
+import { IconHome, IconDashboard, IconApps, IconFile, IconMessage, IconSend, IconStorage, IconUser, IconExport, IconSettings } from '@arco-design/web-vue/es/icon'
+
+const router = useRouter()
+const route = useRoute()
+const userStore = useUserStore()
+const collapsed = ref(false)
+
+const titleMap = {
+  'merchant-overview': '数据概览',
+  'merchant-products': '商品管理',
+  'merchant-orders': '订单管理',
+  'merchant-reviews': '评价管理',
+  'merchant-logistics': '物流管理',
+  'merchant-inventory': '库存管理',
+  'merchant-profile': '个人信息'
+}
+
+const onMenuClick = (key) => {
+  router.push({ name: key })
+}
+
+const goHome = () => router.push('/')
+const goProfile = () => router.push({ name: 'merchant-profile' })
+const logout = async () => {
+  await userStore.logout()
+  router.replace('/login')
+}
+
+onMounted(async () => {
+  await userStore.fetchMe()
+  if (userStore.role !== 'MERCHANT') {
+    router.replace('/login')
+  }
+})
+</script>
+
+<style scoped>
+.merchant-layout { background: #f0f2f5; }
+.merchant-sider { background: #001529; }
+.sider-header { height: 64px; display: flex; align-items: center; justify-content: center; gap: 10px; padding: 0 16px; border-bottom: 1px solid rgba(255,255,255,0.1); }
+.sider-title { font-size: 16px; font-weight: 600; color: #fff; }
+.merchant-main { background: #f0f2f5; }
+.merchant-header { background: #fff; padding: 0 24px; display: flex; align-items: center; justify-content: space-between; box-shadow: 0 1px 4px rgba(0,0,0,0.1); }
+.page-title { font-size: 18px; font-weight: 600; color: #1f2937; }
+.merchant-content { padding: 20px; overflow: auto; }
+</style>