Nix modules: change docspell user to be a normal user

Seems that unoconv requires a shell.

nix/module-joex.nix

@@ -600,7 +600,9 @@ in {
 
     users.users."${user}" = mkIf (cfg.runAs == null) {
       name = user;
-      isSystemUser = true;
+      isSystemUser = false;
+      createHome = true;
+      home = "/var/docspell";
       description = "Docspell user";
     };
 
@@ -613,7 +615,6 @@ in {
           description = "Unoconv Listener";
           after = [ "networking.target" ];
           wantedBy = [ "multi-user.target" ];
-          path = [ pkgs.unoconv ];
           serviceConfig = {
             Restart = "always";
           };