Apply coredata rules: idempotent deletes and constraint checks

Delete methods no longer check RowsAffected — deletes are
idempotent. PgError handlers now check both error code and
constraint name to avoid misattributing violations. Also
migrated remaining errors.As patterns to errors.AsType.

Signed-off-by: Émile Ré <emile@probo.com>

pkg/coredata/access_review_campaign.go

@@ -233,15 +233,11 @@ WHERE %s AND id = @id
 	args := pgx.StrictNamedArgs{"id": c.ID}
 	maps.Copy(args, scope.SQLArguments())
 
-	result, err := conn.Exec(ctx, q, args)
+	_, err := conn.Exec(ctx, q, args)
 	if err != nil {
 		return fmt.Errorf("cannot delete access_review_campaign: %w", err)
 	}
 
-	if result.RowsAffected() == 0 {
-		return ErrResourceNotFound
-	}
-
 	return nil
 }