error: 'CGDisplayCreateImageForRect' is unavailable: obsoleted in macOS 15.0 - Please use ScreenCaptureKit instead

Building laf, as part of building Aseprite 1.3.8.1, fails when using the macOS 15.0 deployment target, which is the default when building on macOS 15:

```
laf/os/osx/system.mm:118:22: error: 'CGDisplayCreateImageForRect' is unavailable: obsoleted in macOS 15.0 - Please use ScreenCaptureKit instead.
118 | CGImageRef image = CGDisplayCreateImageForRect(CGMainDisplayID(),
| ^
```

A workaround is to tell the build to use the macOS 14.0 deployment target (or earlier) by adding the flag `-DCMAKE_OSX_DEPLOYMENT_TARGET=14.0` when running `cmake`.

Start in laf/os/osx/system.mm at line 118 and inspect the CGDisplayCreateImageForRect call and its surrounding screen-capture path. Build laf with the macOS 15.0 deployment target to reproduce the failure; done means the macOS 15 build succeeds using the requested ScreenCaptureKit replacement rather than the obsolete API.

Written by the indexing model from the issue text.