EUI Gallery 1.3.1

1. Add bundled sample images to avatar, carousel, image preview, upload, comparison, and visual effect examples.
2. Fix CMake and Ninja discovery when preparing the Qt 6 runtime from macOS GUI applications.
3. Show an animated progress bar during Qt 6 preparation and measured percentages during installation.
4. Fix indeterminate progress so segments wrap continuously from the right edge to the left.
5. Load image preview thumbnails only when needed and trigger the image error example on demand.