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>

kernels/ContentFill.h

@@ -0,0 +1,4 @@
+#include <stddef.h>
+#include <stdint.h>
+// Returns 1 on success, 0 when no source patch exists, -1 on allocation failure.
+int content_fill(uint8_t *rgba, size_t stride, const uint8_t *mask, size_t maskStride, int width, int height);