feat(auth): 后台登录、角色权限与会话访问策略

管理员与客服分角色登录，权限由后端判定；前端补齐登录、人员与组织管理页面。

frontend/src/utils/apiError.ts

@@ -0,0 +1,38 @@
+/*
+Copyright 2024-2026 ChatterMate
+
+Licensed under the Apache License, Version 2.0 (the "License");
+you may not use this file except in compliance with the License.
+You may obtain a copy of the License at
+
+    http://www.apache.org/licenses/LICENSE-2.0
+
+Unless required by applicable law or agreed to in writing, software
+distributed under the License is distributed on an "AS IS" BASIS,
+WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+See the License for the specific language governing permissions and
+limitations under the License.
+*/
+
+/** One validation problem in FastAPI's 422 body. */
+interface ValidationDetail {
+  msg?: string
+}
+
+/**
+ * A sentence to show for a failed API call. FastAPI sends `detail` as a
+ * string for errors we raise, but as a list of objects for request
+ * validation (422) - shown raw, that list reads "[object Object]".
+ */
+export function apiErrorMessage(error: any, fallback: string): string {
+  const data = error?.response?.data
+  const detail = data?.detail
+  if (typeof detail === 'string' && detail) return detail
+  if (Array.isArray(detail)) {
+    const msg = (detail as ValidationDetail[]).find((d) => typeof d?.msg === 'string')?.msg
+    // Pydantic prefixes a validator's own message with "Value error, "
+    if (msg) return msg.replace(/^Value error, /, '')
+  }
+  if (typeof data?.message === 'string' && data.message) return data.message
+  return fallback
+}