用户消息系统：消息列表、订单群聊、联系对方入口

- 新增消息列表页和聊天详情页，支持 SSE 实时推送
- 订单详情页新增"联系对方"按钮，一键进入订单群聊
- 导航栏新增"消息"入口
- 修复 mobileHost 路径匹配 bug，避免 /m 前缀误匹配
- 优化 dev.sh：提取 mysql 辅助函数、修复空 PID 处理、条件检查依赖

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

frontend/src/layouts/AppLayout.vue

@@ -3,6 +3,7 @@ import { ref } from "vue";
 import { useRouter } from "vue-router";
 import {
   Bell,
+  ChatDotRound,
   CirclePlus,
   House,
   Search,
@@ -21,6 +22,7 @@ const navItems = [
   { label: "首页", to: "/", icon: House },
   { label: "租号大厅", to: "/listings", icon: Shop },
   { label: "我的订单", to: "/orders", icon: Tickets },
+  { label: "消息", to: "/messages", icon: ChatDotRound },
   { label: "钱包", to: "/wallet", icon: Wallet },
 ];