Help Wanted: Need GUI!

## Need GUI for non-coders.

### it should be
* simple
* clean
* easy to use
* error friendly

YTBackup needs a elegant and simple UI. we already have the complete Command Line Interface, we just need to do some UI magic and also handle errors and expections.

### user should
* **Backup**
* select destination folder
* specify destination file name
* **Restore**
* select YTBackup JSON file
* specifying destination folder
* showing thumbnail for current downloading Video
* ability to skip video downloads
* throw friendly error if something goes wrong, but without terminating the whole download process
* pausing and resuming downloading

## Basic Low Fidelity Design

Start by reading the existing Command Line Interface and the linked low-fidelity design to understand the current backup and restore flows. Define the GUI scope around destination and file selection, restore controls, thumbnail display, pausing, skipping, and error handling. Done requires an agreed design and a working interface covering these behaviors without terminating the whole download process.

Written by the indexing model from the issue text.