Stop-linking-a-repository-readers-cannot-open

The readme pointed at github.com/agentrust-io/trace-registry twice, in the
header nav and in the resources table. That repository is private, so both links
return 404 for every reader of a public readme.

Drop the nav entry and keep the resources row without a link, saying plainly
that it is not public yet. That keeps the fact that a registry exists, which is
worth knowing, without sending anyone to a 404. If the repository is opened, the
link goes back.

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>

Author: imran-siddique

README.md

@@ -14,7 +14,6 @@
   <a href="spec/trace-v0.2.md">Specification</a> &nbsp;|&nbsp;
   <a href="schema/trace-claim.json">Schema</a> &nbsp;|&nbsp;
   <a href="examples/">Examples</a> &nbsp;|&nbsp;
-  <a href="https://github.com/agentrust-io/trace-registry">Registry</a> &nbsp;|&nbsp;
   <a href="https://github.com/agentrust-io/trace-tests">Test Suite</a> &nbsp;|&nbsp;
   <a href="https://github.com/agentrust-io/cmcp">Reference Impl</a>
 </p>
@@ -72,7 +71,7 @@ signed = sign_record(record, key=signing_key)
 | 🔍 Schema | [schema/trace-claim.json](schema/trace-claim.json) |
 | 📦 PyPI | [agentrust-trace](https://pypi.org/project/agentrust-trace/) |
 | 🧪 Test suite | [trace-tests](https://github.com/agentrust-io/trace-tests) |
-| 🗂 Registry | [trace-registry](https://github.com/agentrust-io/trace-registry) |
+| 🗂 Registry | `trace-registry` (not public yet) |
 | 🔗 Reference implementation | [cmcp](https://github.com/agentrust-io/cmcp) |
 | 💬 Discussions | [GitHub Discussions](https://github.com/orgs/agentrust-io/discussions) |
 | 📋 Changelog | [CHANGELOG.md](CHANGELOG.md) |