fix(sync): authenticate PR creation via a repo-scoped GitHub App - #14

Node.js 20 is deprecated. The following actions target Node.js 20 but are being forced to run on Node.js 24: actions/checkout@11d5960a326750d5838078e36cf38b85af677262, actions/upload-artifact@ea165f8d65b6e75b540449e92b4886f43607fa02, astral-sh/setup-uv@caf0cab7a618c569241d31dcd442f54681755d39. For more information see: https://github.blog/changelog/2025-09-19-deprecation-of-node-20-on-github-actions-runners/

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