Broken link to ravyn.dev encoders example in docs #976

The link at docs/index.rst:142 points to https://www.ravyn.dev/encoders/#example, but the #example fragment no longer exists on that page. The correct anchor appears to be #complete-custom-encoder-example.

This causes the link checker CI job to fail on all PRs.