fix(readme): use raw HTML for README-CLAUDE link

The previous absolute URL pointed at the example repo's main branch,
which won't have README-CLAUDE.md until the example is regenerated
with add_claude=yes — chicken-and-egg, so linkcheck 404s.

Raw <a href="./README-CLAUDE.md"> works in both renderers without that
dependency:
- myst: passes through as inline HTML, no xref_missing warning.
- sphinx linkcheck: doesn't follow raw HTML hrefs (verified locally),
  so no 404.
- GitHub: renders as a normal clickable link to the file in the repo.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

Author: gilesknap

template/README.md.jinja

@@ -16,7 +16,7 @@ how it does it, and why people should use it.
 {% if pypi                   %}PyPI            | `pip install {{distribution_name}}`
 {% endif %}{% if docker      %}Docker          | `docker run ghcr.io/{{github_org | lower}}/{{repo_name}}:latest`
 {% endif %}{% if sphinx      %}Documentation   | <{{docs_url}}>
-{% endif %}{% if add_claude  %}Claude sandbox  | [README-CLAUDE.md]({{repo_url}}/blob/main/README-CLAUDE.md)
+{% endif %}{% if add_claude  %}Claude sandbox  | <a href="./README-CLAUDE.md">README-CLAUDE.md</a>
 {% endif                     %}Releases        | <{{repo_url}}/releases>
 
 This is where you should put some images or code snippets that illustrate