feat: Features架构迁移 - P0和P1部分完成

## 完成的工作

### P0: 基础设施准备
- 创建 features/ 和 shared/ 目录结构
- 迁移共享资源：API基础设施、工具函数、类型定义
- 迁移通用composables：useMoney, useSmsCountdown, usePricingCalculator
- 迁移全局样式文件
- 建立模块化导出系统

### P1.1: 钱包模块 (wallet)
- 迁移 API: wallet.ts
- 迁移 Views: WalletView.vue
- 新增 Composable: useWallet.ts (封装钱包状态管理)
- 更新导入路径到 shared/

### P1.2: 聊天模块 (chats)
- 迁移 API: chats.ts
- 迁移 Views: ChatView, MessagesView (桌面+移动)
- 迁移 Composables: useChatSSE.ts
- 迁移 Components: ChatAttachmentImage.vue
- 更新导入路径到 shared/

## 技术改进
- 修复 shared/composables 导出问题 (default → 命名导出)
- 修复 shared/api/client.ts 类型导入路径
- 建立清晰的模块边界和导出规范

## 文档
- 添加完整的迁移计划文档
- 添加进度跟踪文档

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

frontend/src/shared/components/layout/MobileBottomNav.vue

@@ -0,0 +1,111 @@
+<script setup lang="ts">
+import { useRoute, RouterLink } from 'vue-router'
+
+const route = useRoute()
+
+function isNavActive(path: string) {
+  if (path === '/m') return route.path === '/m'
+  return route.path.startsWith(path)
+}
+</script>
+
+<template>
+  <nav class="bottom-nav">
+    <RouterLink
+      to="/m"
+      class="nav-item"
+      :class="{ active: isNavActive('/m') }"
+    >
+      <van-icon name="home-o" :size="22" />
+      <span>首页</span>
+    </RouterLink>
+    <RouterLink
+      to="/m/messages"
+      class="nav-item"
+      :class="{ active: isNavActive('/m/messages') }"
+    >
+      <van-icon name="chat-o" :size="22" />
+      <span>消息</span>
+    </RouterLink>
+    <RouterLink to="/m/seller/listings/create" class="nav-item nav-publish">
+      <div class="publish-pill">+</div>
+      <span>发布</span>
+    </RouterLink>
+    <RouterLink
+      to="/m/orders"
+      class="nav-item"
+      :class="{ active: isNavActive('/m/orders') }"
+    >
+      <van-icon name="orders-o" :size="22" />
+      <span>订单</span>
+    </RouterLink>
+    <RouterLink
+      to="/m/profile"
+      class="nav-item"
+      :class="{ active: isNavActive('/m/profile') }"
+    >
+      <van-icon name="manager-o" :size="22" />
+      <span>我的</span>
+    </RouterLink>
+  </nav>
+</template>
+
+<style scoped>
+.bottom-nav {
+  position: fixed;
+  left: 0;
+  right: 0;
+  bottom: 0;
+  z-index: 100;
+  display: flex;
+  background: #fff;
+  border-top: 1px solid #eee;
+  padding-bottom: env(safe-area-inset-bottom);
+  height: calc(50px + env(safe-area-inset-bottom));
+  box-sizing: border-box;
+}
+
+.nav-item {
+  flex: 1;
+  display: flex;
+  flex-direction: column;
+  align-items: center;
+  justify-content: center;
+  gap: 2px;
+  color: #999;
+  font-size: 10px;
+  text-decoration: none;
+}
+
+.nav-item.active {
+  color: #1477ff;
+}
+
+.nav-item span {
+  font-weight: 600;
+}
+
+.publish-pill {
+  width: 36px;
+  height: 26px;
+  display: grid;
+  place-items: center;
+  border-radius: 13px;
+  background: #ff6a00;
+  color: #fff;
+  font-size: 18px;
+  font-weight: 900;
+}
+
+.nav-publish span {
+  color: #ff6a00;
+}
+
+/* 响应式适配 */
+@media (min-width: 520px) {
+  .bottom-nav {
+    left: calc((100vw - 430px) / 2);
+    right: calc((100vw - 430px) / 2);
+  }
+}
+</style>