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/document_version_approval_decision.go

@@ -305,9 +305,8 @@ INSERT INTO document_version_approval_decisions (
 
 	_, err := conn.Exec(ctx, q, args)
 	if err != nil {
-		var pgErr *pgconn.PgError
-		if errors.As(err, &pgErr) {
-			if pgErr.Code == "23505" {
+		if pgErr, ok := errors.AsType[*pgconn.PgError](err); ok {
+			if pgErr.Code == "23505" && pgErr.ConstraintName == "document_version_approval_decisions_quorum_id_approver_id_key" {
 				return ErrResourceAlreadyExists
 			}
 		}