[clang-doc] The Mustache HTML output uses full file paths for links

These full paths break web pages if they're opened anywhere but the build machine, because the links are wrong. These should all be relative file paths.

Current HTML:

```html
@nonymous_record_00774ABA8C0A775DA34D65BFF8EE1967BE25FAE3
```

Corrected:

```html
@nonymous_record_00774ABA8C0A775DA34D65BFF8EE1967BE25FAE3
```

CC: @evelez7 I'm guessing this is somehow generated from the json paths. Do you know where in the JSONGenerator or the Mustache bits where the links are generated?

Start by tracing how the JSONGenerator and Mustache parts produce the HTML links; inspect the generated path values shown in the issue. Update the link generation so output uses relative paths rather than the build-machine prefix, then verify the generated HTML matches the corrected example.

Written by the indexing model from the issue text.