Regression: Modern UI rounded corners break edge scrollbar dragging behavior

Does this issue occur when all extensions are disabled?: Yes

- VS Code Version: 1.132.0
- OS Version: Windows_NT x64 10.0.26200

### Steps to Reproduce

1. Open VS Code with a file that has enough content to show the vertical scrollbar.
2. Move the mouse pointer to the far right edge of the screen.
3. Try to grab and drag the scrollbar thumb without precisely targeting it.
4. Notice that the rightmost edge area no longer activates the scrollbar.

### Expected

The scrollbar should remain draggable when the pointer is placed at the extreme right edge of the window, preserving the long-standing desktop interaction pattern where users can "throw" the pointer to the screen edge.

### Actual

The Modern UI rounded corner / increased spacing design leaves a gap between the screen edge and the scrollbar. The rightmost pixels no longer map to the scrollbar hit area, requiring users to precisely aim at the scrollbar thumb.

This is a usability regression caused by the Modern UI redesign.

### Reference

Microsoft Edge maintains compatibility with this interaction pattern by keeping the rightmost edge pixels mapped to the scrollbar hit area even with rounded window corners.

### Suggested fix

Keep the visual spacing and rounded corner design, but add an invisible edge hit area (for example, the outermost 1–2 px adjusted for DPI scaling) that maps to scrollbar interaction.