ci: tolerate release PR creation permission limits

[cbusillo]

Summary

• commit durable release metadata before creating the handoff branch
• remove transient release artifacts/context from the handoff branch
• make gh pr create best-effort so repos that disallow Actions-created PRs still finish with a pushed release branch and warning

Validation

• ruby -e 'require "yaml"; YAML.load_file(".github/workflows/release.yml"); puts "yaml ok"'\n- git diff --check\n- ./build-fast.sh\n\nRefs Fix release preflight runner capabilities #108\nRefs Plan Every Code default branch and release identity #87