Return campaign status sentinels without wrapping

Drop CampaignStatusError from errors.go and map coredata status to
client errors in the service layer only. Cancel on terminal statuses
uses the same sentinels instead of fmt status strings.

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

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

pkg/accessreview/errors_test.go

@@ -21,15 +21,13 @@
 package accessreview
 
 import (
-	"errors"
-	"fmt"
 	"testing"
 
 	"github.com/stretchr/testify/assert"
 	"go.probo.inc/probo/pkg/coredata"
 )
 
-func TestCampaignStatusError(t *testing.T) {
+func TestCampaignNotDraftError(t *testing.T) {
 	t.Parallel()
 
 	tests := []struct {
@@ -46,8 +44,7 @@ func TestCampaignStatusError(t *testing.T) {
 		t.Run(string(tt.status), func(t *testing.T) {
 			t.Parallel()
 
-			err := fmt.Errorf("cannot start campaign: %w", CampaignStatusError(tt.status))
-			assert.ErrorIs(t, err, tt.want)
+			assert.ErrorIs(t, campaignNotDraftError(tt.status), tt.want)
 		})
 	}
 }