internal/rosa/package: migrate system image

The overlay argument also enables migration of stage0.

Signed-off-by: Ophestra <cat@gensokyo.uk>

internal/rosa/package/images/package.az

@@ -19,3 +19,27 @@ package initramfs-image {
 		gen_init_cpio,
 	];
 }
+
+package system-image {
+	description = "Rosa OS system image";
+	version = unversioned;
+	exclude = true;
+
+	source = earlyinit;
+	extra = [
+		musl,
+		mksh,
+		toybox,
+
+		kmod,
+		kernel,
+		firmware,
+	];
+	overlay = "/mnt";
+
+	exec = generic {
+		build = "mksquashfs /mnt/system /work/system.img";
+	};
+
+	inputs = [ squashfs-tools ];
+}