fix(clients): persist group for node-inbound clients

The client create/edit form left `group` out of the request payload, so choosing a group in the form was silently dropped (bulkAdd from the Groups page still worked because it writes the column directly). Add `group` to the payload next to `comment`.

SyncInbound also overwrote group_name unconditionally; a group set via bulkAdd is never pushed to the node, so the next node snapshot — which lacks it — wiped the column. Keep group sticky (only overwrite when the incoming value is non-empty); group is only ever set/cleared via the Groups page. Preserve comment for node clients during snapshot sync the same way. Add tests.

web/service/client.go

@@ -237,7 +237,9 @@ func (s *ClientService) SyncInbound(tx *gorm.DB, inboundId int, clients []model.
 			row.ExpiryTime = incoming.ExpiryTime
 			row.Enable = incoming.Enable
 			row.TgID = incoming.TgID
-			row.Group = incoming.Group
+			if incoming.Group != "" {
+				row.Group = incoming.Group
+			}
 			row.Comment = incoming.Comment
 			row.Reset = incoming.Reset
 			if incoming.CreatedAt > 0 && (row.CreatedAt == 0 || incoming.CreatedAt < row.CreatedAt) {