HF RL Explorer

Add uiOpenFolder() for folder selection dialog

Add uiOpenFolder() for folder selection dialog: a task in LegoFlow-SWE (Harbor dataset). The library already provides uiOpenFile() and uiSaveFile() to let the user choose files. It would be helpful to have a similar function for choosing a directory.

The task

The library already provides `uiOpenFile()` and `uiSaveFile()` to let the user choose files. It would be helpful to have a similar function for choosing a directory.

Part of Lego-X/LegoFlow-SWE.