支持可配置的会话自动分配策略

- 租户可设置负载最低或轮询，以及每位坐席最大进行中会话数
- 自动分配按策略过滤在线一线客服，满并发则保持排队
- 系统设置「客服分配规则」页可保存上述配置

web/src/services/api.ts

@@ -318,6 +318,8 @@ export const deleteStaff = (id: number) => del(`/staff/${id}`)
 
 // Tenant settings
 export type WorkHours = Record<string, string>
+export type AssignStrategy = 'least_load' | 'round_robin'
+
 export interface TenantSettings {
   tenant_id: number
   display_name: string
@@ -330,6 +332,10 @@ export interface TenantSettings {
   notify_new_session: boolean
   notify_offline_leave: boolean
   notify_daily_report: boolean
+  /** least_load 负载最低 | round_robin 轮询 */
+  assign_strategy?: AssignStrategy
+  /** 每位坐席最大进行中会话数，0=不限制 */
+  max_active_per_agent?: number
 }
 export const getTenantSettings = () => get<TenantSettings>('/settings')
 export const updateTenantSettings = (data: Partial<TenantSettings> & { work_hours?: WorkHours }) =>