Support customizing Padding and Margin.

**Is your feature request related to a problem? Please describe.**
I wanna hide the window bar but still keep the top padding like in this picture.

**Describe the solution you'd like**
Support Settings like:
```
Set PaddingTop 20
Set PaddingBottom 20
Set PaddingLeft 20
Set PaddingRight 20
Set MarginTop 20
Set MarginBottom 20
Set MarginLeft 20
Set MarginRight 20
```

**Describe alternatives you've considered**
Idk, maybe hide window bar?

The issue names no files or tests. Start by locating how VHS parses Set settings and applies window-bar, padding, and margin layout; then trace the rendering path to determine where the eight values belong. Done means each requested setting is accepted and visibly changes the recorded window layout, with coverage for the new settings.

Written by the indexing model from the issue text.