Generally ui.frontend is only used to generate/build your front end code (CSS and JS), the generated output or code you will place it in ui.apps clientlibs.
So, it is not required or it is not allowed to add ui.frontend and update directly to the AEM server
ui.frontend- (optional) contains the artifacts required to use the Webpack-based front-end build module.
We will commit the code to a source repository (git,bitbucket etc)