Use SvelteKit render function for templating and add error page

nix/package.nix

@@ -32,23 +32,12 @@ let
       cp -r db/migrations/* $out/rest-api/db/migrations
     '';
   };
-
-  templates = stdenv.mkDerivation {
-    inherit pname version;
-    name = "archtika-templates";
-    src = ../templates;
-    installPhase = ''
-      mkdir -p $out/templates
-      cp -r * $out/templates
-    '';
-  };
 in
 symlinkJoin {
   name = pname;
   paths = [
     web
     api
-    templates
   ];
 
   meta = with lib; {