Update react-native to v20.1.3 (#28)

* Update react-native to v20.1.3

* Pin react-test-renderer to bundled renderer 19.2.3

react-test-renderer was left at 19.2.7 while react and the renderer
bundled in react-native 0.85.3 are both 19.2.3. react-test-renderer
must exactly match the bundled react-native-renderer (same constraint
that pins `react`), so align it to 19.2.3.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

* Add PR-body reminder to manually pin react on react-native bumps

The react-native group PR does not touch react/react-test-renderer
(they're disabled in Renovate and pinned by hand to the bundled
renderer). Attach a prBodyNotes reminder so the manual alignment step
surfaces in every react-native PR instead of relying on memory.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

* Reframe react-native PR note around the dependency coupling

Lead with which packages must move together (react/react-test-renderer
vs the bundled renderer) instead of narrating the merge workflow.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

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Co-authored-by: Renovate Bot <bot@renovateapp.com>
Co-authored-by: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

Author: 3 people