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

server/internal/handler/settings.go

@@ -60,6 +60,8 @@ func getOrCreateTenantSettings(tenantID uint) (*model.TenantSetting, error) {
 		NotifyNewSession:   true,
 		NotifyOfflineLeave: true,
 		NotifyDailyReport:  false,
+		AssignStrategy:     assignStrategyLeastLoad,
+		MaxActivePerAgent:  0,
 	}
 	if err := model.DB.Create(&setting).Error; err != nil {
 		return nil, err
@@ -135,18 +137,25 @@ func isWithinWorkHours(setting *model.TenantSetting, now time.Time) bool {
 }
 
 func settingsResponse(setting *model.TenantSetting) gin.H {
+	strategy := normalizeAssignStrategy(setting.AssignStrategy)
+	maxActive := setting.MaxActivePerAgent
+	if maxActive < 0 {
+		maxActive = 0
+	}
 	return gin.H{
-		"tenant_id":            setting.TenantID,
-		"display_name":         setting.DisplayName,
-		"agent_nickname":       setting.AgentNickname,
-		"timezone":             setting.Timezone,
-		"welcome_message":      setting.WelcomeMessage,
-		"offline_prompt":       setting.OfflinePrompt,
-		"work_hours":           parseWorkHours(setting.WorkHoursJSON),
-		"worktime_prompt":      setting.WorktimePrompt,
-		"notify_new_session":   setting.NotifyNewSession,
-		"notify_offline_leave": setting.NotifyOfflineLeave,
-		"notify_daily_report":  setting.NotifyDailyReport,
+		"tenant_id":             setting.TenantID,
+		"display_name":          setting.DisplayName,
+		"agent_nickname":        setting.AgentNickname,
+		"timezone":              setting.Timezone,
+		"welcome_message":       setting.WelcomeMessage,
+		"offline_prompt":        setting.OfflinePrompt,
+		"work_hours":            parseWorkHours(setting.WorkHoursJSON),
+		"worktime_prompt":       setting.WorktimePrompt,
+		"notify_new_session":    setting.NotifyNewSession,
+		"notify_offline_leave":  setting.NotifyOfflineLeave,
+		"notify_daily_report":   setting.NotifyDailyReport,
+		"assign_strategy":       strategy,
+		"max_active_per_agent":  maxActive,
 	}
 }
 
@@ -175,6 +184,8 @@ type updateSettingsReq struct {
 	NotifyNewSession   *bool             `json:"notify_new_session"`
 	NotifyOfflineLeave *bool             `json:"notify_offline_leave"`
 	NotifyDailyReport  *bool             `json:"notify_daily_report"`
+	AssignStrategy     *string           `json:"assign_strategy"`
+	MaxActivePerAgent  *int              `json:"max_active_per_agent"`
 }
 
 func (h *SettingsHandler) Update(c *gin.Context) {
@@ -284,6 +295,21 @@ func (h *SettingsHandler) Update(c *gin.Context) {
 	if req.NotifyDailyReport != nil {
 		updates["notify_daily_report"] = *req.NotifyDailyReport
 	}
+	if req.AssignStrategy != nil {
+		raw := strings.TrimSpace(*req.AssignStrategy)
+		if raw != assignStrategyLeastLoad && raw != assignStrategyRoundRobin {
+			c.JSON(http.StatusBadRequest, gin.H{"code": 400, "message": "分配策略无效，可选 least_load / round_robin"})
+			return
+		}
+		updates["assign_strategy"] = raw
+	}
+	if req.MaxActivePerAgent != nil {
+		if *req.MaxActivePerAgent < 0 || *req.MaxActivePerAgent > 200 {
+			c.JSON(http.StatusBadRequest, gin.H{"code": 400, "message": "最大并发需为 0–200（0 表示不限制）"})
+			return
+		}
+		updates["max_active_per_agent"] = *req.MaxActivePerAgent
+	}
 	if len(updates) == 0 {
 		c.JSON(http.StatusBadRequest, gin.H{"code": 400, "message": "没有可更新字段"})
 		return