ci: add docker image build

flake.nix

@@ -13,6 +13,12 @@
         overlays.avcpp = final: prev: {
           avcpp = final.callPackage ./nix/avcpp.nix {};
         };
+        overlays.lib = final: prev: {
+          lib = prev.lib.extend (_: _:
+            import ./nix/lib.nix {
+              inherit (final) lib;
+            });
+        };
       };
       systems = [
         "x86_64-linux"
@@ -28,12 +34,14 @@
           overlays = [
             self.overlays.mosh-me
             self.overlays.avcpp
+            self.overlays.lib
           ];
           config = {};
         };
 
         packages.default = pkgs.mosh-me;
         packages.mosh-me = pkgs.mosh-me;
+        packages.docker = pkgs.callPackage ./nix/docker.nix {tag = pkgs.lib.gitRevOrLastModified self;};
 
         devShells.default = self'.devShells.mosh-me;
         devShells.mosh-me = pkgs.mkShell {