Link to the JS Implementation is incorrect

In the top level README, the link to a "sample JavaScript" implementation is broken. It links to an HTML page that shows the inputs and outputs, not the actual sample implemantion code.

```
- [JavaScript Implementation](./llmstxt-js.html) - Sample JavaScript implementation
```

Open the top-level README and inspect the referenced llmstxt-js.html page alongside the repository's JavaScript sample implementation. Update the JavaScript Implementation link to point to the actual sample code, then verify that the README link resolves to that implementation.

Written by the indexing model from the issue text.