chore(ui): refactor sveltekit api endpoints to follow better error handling pattern

[andrewrisse]

Check all SvelteKit API endpoint to ensure they follow a similar pattern for error handling (both validation, and catch all errors).

Follow the pattern in api/audio/translation/+server.ts

Blocked by #1046

ex. validation:

catch (e) {
    console.error(e);
    error(400, { message: `${e}` });
  }

catch (e) {
  return handleError(e);
}

This will allow frontend components to handle validation vs other errors