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/LayerMaskMenu.h

@@ -0,0 +1,18 @@
+#pragma once
+#include "Document/EditorSession.h"
+#include <QToolButton>
+
+// One click adds a mask: white, or the selection black.
+class LayerMaskMenu : public QToolButton {
+    Q_OBJECT
+public:
+    explicit LayerMaskMenu(EditorSession &session, QWidget *parent = nullptr);
+
+protected:
+    void changeEvent(QEvent *event) override;
+
+private:
+    void synchronize();
+
+    EditorSession &m_session;
+};