fix(groups): keep group traffic totals stable across client resets and deletes

ListGroups displays live_sum(client_traffics) minus the group's stored
reset baseline, but only ResetGroupTraffic ever moved the baseline. Any
client-level operation that zeroed or deleted traffic rows (single/bulk
reset, client delete, removing a client's last inbound) shrank the live
sum and silently subtracted that client's history from the group total.

Shift the baseline down by the removed counters inside the same
transaction, so group totals only change through group reset. Derived
groups without a stored row get one with a negative baseline, which the
existing clamp handles.

Closes #5675

internal/web/service/client_bulk.go

@@ -834,6 +834,9 @@ func (s *ClientService) BulkDelete(inboundSvc *InboundService, emails []string,
 		// Serialize the row cleanup against the traffic poll to avoid the
 		// cross-transaction lock-order deadlock on client_traffics/inbounds.
 		if err := runSerializedTx(func(tx *gorm.DB) error {
+			if e := adjustGroupBaselinesForRemovedTraffic(tx, successEmails); e != nil {
+				return e
+			}
 			for _, batch := range chunkInts(successIds, sqlInChunk) {
 				if e := tx.Where("client_id IN ?", batch).Delete(&model.ClientInbound{}).Error; e != nil {
 					return e