CFC: Updating links to `object`, `image`, and `relationship` in Activity Vocabulary

The Activity Vocabulary has a number of terms that only differ by
capitalization: Object/object, Image/image, and Relationship/relationship.
The spec library we use, reSpec, generates links by lowercasing the term,
making non-unique links for these terms. The issue is here:

https://github.com/w3c/activitystreams/issues/497

This is just a markup change, not a change that matters for the meaning of
the specification, so I think we don't need an erratum, and can simply
update the spec document directly. This PR on the as2 repo manually adds
link targets for the lowercase terms, making the links work correctly:

https://github.com/w3c/activitystreams/pull/548

This is a call for consensus on making this markup change to the Activity
Vocabulary document. Barring objections in two weeks (5 Dec 2025, end of
day, anywhere on earth), I will merge this PR and update the working draft
of AS2 Vocabulary.

Evan