Update repository references on 0.86

[cipolleschi]

Summary

• update release and GitHub automation from facebook/react-native to react/react-native
• update package metadata, podspec sources, repository utilities, tests, snapshots, documentation, and historical links
• preserve references to separate repositories such as facebook/react-native-website and facebook/react-native-devtools-frontend

This removes every remaining reference to the old core repository slug from the 0.86 release line. In particular, draft release creation, changelog PR creation, release asset URLs, and release-testing API calls now target the current organization.

Test plan

• yarn test .github/workflow-scripts/__tests__/createDraftRelease-test.js .github/workflow-scripts/__tests__/generateChangelog-test.js --runInBand (20 tests passed)
• yarn test scripts/releases/__tests__/upload-release-assets-for-dotslash-test.js scripts/releases/__tests__/write-dotslash-release-asset-urls-test.js --runInBand (12 tests and 23 snapshots passed)
• codegen generator assertions passed (42 tests and 24 snapshots); local cleanup hit the pre-existing removal of fs.rmdirSync({recursive: true}) in the installed Node version
• parsed every changed package.json
• verified every modification is exactly the intended slug substitution
• verified no old core facebook/react-native repository reference remains
• git diff --check

Changelog:

[INTERNAL] - Update React Native repository references on the 0.86 release line.