I will be crucified by this, but I think you are doing it wrong.

I would split it in 2 steps.

First, just move it to svelte, maintain the same functionality and ideally wrap it into some tests. As mentioned you want something that can be used as pass/no-pass filter. As in yes, the code did not change the functionality.

Then, apply another pass from Svelte bad quality to Svelte good quality. Here the trick is that "good quality" is quite different and subjective. I found the models not quite able to grasp what "good quality" means in a codebase.

For the second pass, ideally you would feed an example of good modules in your codebase to follow and a description of what you think it is important.