feat(ci): use nix to build extension zip

.forgejo/workflows/build-ext.yml

@@ -15,9 +15,9 @@ jobs:
       - name: Checkout code
         uses: actions/checkout@v4
       - name: Build extension
-        run: ./build-ext.sh
+        run: nix build .#extension
       - name: Upload extension
         uses: actions/upload-artifact@v4
         with:
           name: aci-ext.zip
-          path: aci-ext.zip
+          path: result

flake.nix

@@ -39,6 +39,18 @@
             WorkingDir = "/state";
           };
         };
+
+        extension = pkgs.stdenv.mkDerivation {
+          name = "aci-extension.zip";
+          inherit version;
+          src = ./extension;
+          phases = "installPhase";
+          nativeBuildInputs = [ pkgs.zip ];
+          installPhase = ''
+          cd $src/
+          zip -r $out *
+          '';
+        };
       };
       devShells.default = pkgs.mkShell {
         nativeBuildInputs = with pkgs; [