feat: 迁入 MiGu.Server、平台前端与车辆列表 reflection 回退

从 Simple-FR 拆出 Platform.Server 并重命名为 MiGu.Server；frontends 源码与构建脚本迁入本仓库。地图监控在 projection/cars 失败或为空时回退 reflection 车辆列表；Simple 仓库已移除旧 Platform.Server。

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

frontends/apps/simple-platform-vue/src/components/ScopeSwitcher.vue

@@ -0,0 +1,37 @@
+<template>
+  <el-radio-group v-model="current" size="small" @change="onChange">
+    <el-radio-button label="Platform">管理员</el-radio-button>
+    <el-radio-button label="RCSMonitor">运营</el-radio-button>
+  </el-radio-group>
+</template>
+
+<script setup lang="ts">
+import { computed } from 'vue'
+import { useRouter } from 'vue-router'
+import { ElMessage } from 'element-plus'
+import { useAuthStore } from '@/stores/auth'
+import type { Scope } from '@/types/auth'
+
+const auth = useAuthStore()
+const router = useRouter()
+
+// 会话 45 AR-6：switchScope 已变成异步（调后端 /auth/switch-scope）。
+// computed.set 不能 await，只能 fire-and-forget 并在 catch 里弹错。
+const current = computed<Scope>({
+  get: () => auth.scope ?? 'Platform',
+  set: (v) => { void switchAndNavigate(v) }
+})
+
+async function onChange(v: string | number | boolean | undefined) {
+  await switchAndNavigate(v as Scope)
+}
+
+async function switchAndNavigate(scope: Scope) {
+  try {
+    await auth.switchScope(scope)
+    router.push(scope === 'Platform' ? '/admin/map-monitor' : '/monitor/map')
+  } catch (err) {
+    ElMessage.error((err as Error)?.message ?? `切换到 ${scope} 失败`)
+  }
+}
+</script>