refactor(admin): 合并管理后台并移除 apps/agent

- 平台与代理共用 apps/admin，统一登录 manage/auth/login
- 按 userType 展示菜单，修复 token 循环跳转
- 删除独立 apps/agent 前端工程

Co-authored-by: Cursor <cursoragent@cursor.com>

apps/admin/src/views/HomeEntry.vue

@@ -0,0 +1,12 @@
+<script setup lang="ts">
+import { useAuthStore } from '../stores/auth';
+import AdminDashboard from './Dashboard.vue';
+import AgentDashboard from './agent/Dashboard.vue';
+
+const auth = useAuthStore();
+</script>
+
+<template>
+  <AdminDashboard v-if="auth.isAdmin" />
+  <AgentDashboard v-else />
+</template>