Fix undefined source in AddCampaignSource

Declare AccessReviewSource before LoadByID so the package compiles
after RemoveCampaignSource cleanup.

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

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

pkg/accessreview/campaign_service.go

@@ -240,6 +240,8 @@ func (s *Service) AddCampaignSource(
 			if campaign.Status != coredata.AccessReviewCampaignStatusDraft {
 				return NewCampaignNotDraftError(campaign.ID)
 			}
+
+			source := &coredata.AccessReviewSource{}
 			if err := source.LoadByID(ctx, conn, scope, req.AccessReviewSourceID); err != nil {
 				if errors.Is(err, coredata.ErrResourceNotFound) {
 					return coredata.ErrResourceNotFound