Modality Directory Picker Should Span the Full Width of the Form

**Describe the bug**
The modality directory `FileEdit` widget is too narrow and does not span the form’s width, making long paths difficult to read.

**To Reproduce**
1. Open the Data Transfer Lite UI.
2. Observe the directory picker’s limited horizontal width.

**Expected behavior**
The modality directory picker should span across the full form width for readability and consistency with other fields.

**Screenshots**

**Additional context**
Add any other context about the problem here.