fix: clear a stale organisation_role when a user's organisation changes in the admin

The members relation manager and the organisation field of the Users form
declare cabana ClearOnChange on organisation_role: adding or removing a
member, and a form save that moves a user to another organisation or to
none, clear the role unless the same save writes it. Needs a SummerCMS
release with ClearOnChange.

controllers/organisations_admin_controller.go

@@ -23,8 +23,9 @@ const membersRelation = "members"
 // manager. The screen and every write need golem15.users.access_users, as in
 // PHP.
 //
-// The members manager sets and clears users.organisation_id and nothing
-// else. It never writes users_groups.
+// The members manager sets and clears users.organisation_id, and clears
+// users.organisation_role with it (a role belongs to one organisation). It
+// never writes users_groups.
 type organisationsAdminController struct {
 	app appAccess
 }
@@ -73,12 +74,15 @@ func (c organisationsAdminController) requireSlugFormat(ctx context.Context, mod
 // AdminRelationContracts declares the members relation manager: the users
 // whose organisation_id is the organisation. Linking sets the column and
 // unlinking clears it; the column is nullable, so a user is never deleted.
+// Both also clear organisation_role (ClearOnChange), so a role never moves
+// to another organisation or outlives the membership.
 func (organisationsAdminController) AdminRelationContracts() []cabana.RelationContract {
 	return []cabana.RelationContract{{
-		Name:       membersRelation,
-		Kind:       cabana.RelationHasMany,
-		NewRelated: func() any { return &models.User{} },
-		ForeignKey: "organisation_id",
+		Name:          membersRelation,
+		Kind:          cabana.RelationHasMany,
+		NewRelated:    func() any { return &models.User{} },
+		ForeignKey:    "organisation_id",
+		ClearOnChange: []string{"organisation_role"},
 		Columns: map[string]string{
 			"name":  "name",
 			"email": "email",