Dragged captures cannot reach the bottom or right side of screen

When doing manual capture area, the edges can't get closer than one pixel away from the bottom or right side of the display bounds. This extends to the captured image too.

Compositor: niri

<img width="344" height="180" alt="Image" src="https://github.com/user-attachments/assets/9fc029a9-91d1-49ff-9d60-355960f6770c" />