Add validation constraints for repository creation fields (#36671)

Adds validation constraints to repository creation inputs, enforcing
max-length limits for labels/license/readme and enum validation for
trust model and object format. Updates both the API option struct and
the web form struct to keep validation consistent.

services/repository/create.go

@@ -230,6 +230,9 @@ func CreateRepositoryDirectly(ctx context.Context, doer, owner *user_model.User,
 	if opts.ObjectFormatName == "" {
 		opts.ObjectFormatName = git.Sha1ObjectFormat.Name()
 	}
+	if opts.ObjectFormatName != git.Sha1ObjectFormat.Name() && opts.ObjectFormatName != git.Sha256ObjectFormat.Name() {
+		return nil, fmt.Errorf("unsupported object format: %s", opts.ObjectFormatName)
+	}
 
 	repo := &repo_model.Repository{
 		OwnerID:                         owner.ID,