fix(client): delete external-link rows when bulk-deleting clients

The single-client Delete path removes a client's client_external_links rows,
but BulkDelete (and the DelDepleted reaper that routes through it) deleted the
record, mappings and traffic while leaving the external-link rows keyed by the
now-dead client id, so they accumulated as orphans. Delete them in the same
cleanup transaction, keyed by client id like the single path.

internal/web/service/client_bulk.go

@@ -855,6 +855,9 @@ func (s *ClientService) BulkDelete(inboundSvc *InboundService, emails []string,
 				if e := tx.Where("client_id IN ?", batch).Delete(&model.ClientInbound{}).Error; e != nil {
 					return e
 				}
+				if e := tx.Where("client_id IN ?", batch).Delete(&model.ClientExternalLink{}).Error; e != nil {
+					return e
+				}
 			}
 			if !keepTraffic && len(successEmails) > 0 {
 				for _, batch := range chunkStrings(successEmails, sqlInChunk) {