fix: fallback to read access in /sign

Author: KernelDeimos

src/backend/src/routers/sign.js

@@ -117,7 +117,7 @@ module.exports = eggspress('/sign', {
 
         if ( item.action === 'write' ) {
             if ( ! await svc_acl.check(actor, node, 'write') ) {
-                throw await svc_acl.get_safe_acl_error(actor, node, 'write');
+                item.action = 'read';
             }
         }