OmaPhoto 1.0.0: the Linux port of Compositor

A layered image editor for Linux and Omarchy, ported from Compositor
(github.com/robbietilton/Compositor), whose Swift source is its
specification. It reads and writes Compositor's .comp projects.

Packages for Ubuntu, Fedora and Arch come from the release workflow;
scripts/install/ holds one install script per distribution family,
and flake.nix serves NixOS.

Co-Authored-By: Claude <noreply@anthropic.com>

src/UI/CanvasThumbnail.h

@@ -0,0 +1,20 @@
+#pragma once
+#include "Document/LayerTransform.h"
+#include <QImage>
+#include <QPixmap>
+#include <QSizeF>
+
+// Thumbnails framed by the whole canvas, as Photoshop shows them.
+namespace CanvasThumbnail {
+// Pixels per point in the pictures, sharp on scaled displays.
+inline constexpr double backingScale = 2;
+
+// The canvas's shape fitted in a square of `box` points.
+QSize fittedSize(QSizeF canvas, double box);
+// The checkerboard with the pixels placed; null: empty canvas.
+QPixmap layer(const QImage &image, const LayerTransform &transform, QSizeF canvas, double box);
+// The mask placed; its edge tone fills the rest.
+QPixmap mask(const QImage &image, const LayerTransform &transform, QSizeF canvas, double box);
+// The mean gray, 0 to 1, of the outermost pixels.
+double edgeTone(const QImage &image);
+}