Add scope source operation to access review n8n node

Campaigns cannot be started without at least one scope source, but the
n8n node had no way to attach sources after creation. Expose the
addAccessReviewCampaignSource mutation as an Add Source operation so
workflows can configure sources before starting.

Return INVALID instead of INTERNAL when start fails due to missing
sources or invalid status, so n8n surfaces the real error message.

Signed-off-by: Cursor Agent <cursoragent@cursor.com>

Co-authored-by: Bryan FRIMIN <bryan@frimin.fr>

pkg/server/api/console/v1/access_review_campaign_resolvers.go

@@ -9,6 +9,7 @@ import (
 	"context"
 	"errors"
 	"fmt"
+	"strings"
 
 	"github.com/vikstrous/dataloadgen"
 	"go.gearno.de/kit/log"
@@ -796,6 +797,10 @@ func (r *mutationResolver) StartAccessReviewCampaign(ctx context.Context, input
 
 	campaign, err := r.accessReview.StartCampaign(ctx, scope, input.AccessReviewCampaignID)
 	if err != nil {
+		if strings.HasPrefix(err.Error(), "cannot start campaign:") {
+			return nil, gqlutils.Invalid(ctx, err)
+		}
+
 		r.logger.ErrorCtx(ctx, "cannot start access review campaign", log.Error(err))
 
 		return nil, gqlutils.Internal(ctx)