scripts/check_no_gms_signin.sh fails when a pubspec.lock or android
gradle file pulls google_sign_in / play-services-auth / googleid, or a
built APK (--apk) carries GMS auth classes, and names
google_account_token as the fix. install_repo_contract_gate.sh now
installs its shim and an always-run hook in Flutter Android repos.
Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01WzxdWVQE5pYiASpRGgA3Kg
