plandex-server: add git to path

When running `plandex-server` as a service it will panic as it's
unable to find git. Add it to the programs PATH.

pkgs/by-name/pl/plandex-server/package.nix

···
   lib,
   buildGoModule,
   fetchFromGitHub,
+  makeWrapper,
   git,
 }:
 buildGoModule rec {
···
   postInstall = ''
     cp -r migrations $out/migrations
   '';
+
+  postFixup = ''
+    wrapProgram $out/bin/plandex-server \
+      --prefix PATH : ${lib.makeBinPath [ git ]}
+  '';
+
+  nativeBuildInputs = [ makeWrapper ];
 
   nativeCheckInputs = [ git ];