Add changelog entry and update CLAUDE.md PR workflow docs

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

Author: spawnia

.claude/CLAUDE.md

@@ -98,6 +98,6 @@ Follow the [PR template](.github/PULL_REQUEST_TEMPLATE.md):
 
 Add entries to the `## Unreleased` section in [CHANGELOG.md](/CHANGELOG.md).
 Use categories: `Added`, `Changed`, `Deprecated`, `Removed`, `Fixed`, `Security`.
-End each entry with a link to the PR.
+End each entry with a full PR URL: `https://github.com/nuwave/lighthouse/pull/<number>`.
 
 See [CONTRIBUTING.md](/CONTRIBUTING.md) for full guidelines.

CHANGELOG.md

@@ -9,6 +9,10 @@ You can find and compare releases at the [GitHub release page](https://github.co
 
 ## Unreleased
 
+### Fixed
+
+- Fix `upsert` for `HasOne` creating a new record instead of updating when no `id` is provided in the input https://github.com/nuwave/lighthouse/pull/2742
+
 ## v6.64.2
 
 ### Fixed