fix(clients): store client group names trimmed

The groups page lists clients.group_name as stored, while every group
action trims the name it is given. A name with surrounding white space,
saved by a node snapshot or by a client edit, was listed as a separate
group, and deleting, renaming or resetting that row acted on the real
group of the trimmed name instead.

Group names are trimmed wherever a client record is built or updated,
and a one-time seeder folds stored names onto their trimmed form.

internal/database/model/model.go

@@ -1288,7 +1288,7 @@ func (c *Client) ToRecord() *ClientRecord {
 		ExpiryTime:        c.ExpiryTime,
 		Enable:            c.Enable,
 		TgID:              c.TgID,
-		Group:             c.Group,
+		Group:             strings.TrimSpace(c.Group),
 		Comment:           c.Comment,
 		Reset:             c.Reset,
 		ResetDay:          c.ResetDay,