Put 1px mid grey line around windows in non-compositing mode

### Version

20260201

### Explain the issue and what happens

When working with TextEdit, since the bottom and left border of the window are non-existent the white of the TextEdit application blends into any other white space applications (example Workspace Filer)

Having a minimal single line border will improve the visual of TextEdit, making resize by borders easier/more obvious.

### Explain how to reproduce the bug?

Open TextEdit
Position in front of other white window or set desktop background color to white.

### What is the Expected behavior (if applicable)

Applications should present distinct boundaries of their windows.

### Additional context (if applicable)

_No response_

Reproduce the issue by opening TextEdit over another white window or a white desktop background and compare the non-compositing window edges. The issue names no files or tests, so locate the window-decoration path responsible for non-compositing borders; done means a visible 1px mid-grey line around the affected window and no regression in resizing.

Written by the indexing model from the issue text.