docs: add repo-action.md for branches, PRs, upstream syncs and releases
Adds repo-action.md, the rules for how work lands in this fork: ra/main is the release and integration branch, master stays a clean mirror of upstream, every change goes through a PR, upstream comes in by merging a release tag, and releases are annotated tags cut only from ra/main and never moved.
AGENTS.md and CLAUDE.md now open with a note pointing to it, and RUNANYWHERE.md links it.
Branch protection and making ra/main the default branch need an admin, so they aren't part of this PR. Docs only, nothing to build.
Summary by cubic
Adds repo-action.md, the rules for how work lands in this fork: ra/main is the integration and release branch, master stays a clean mirror of upstream, every change goes through a PR, upstream comes in by merging a release tag, and releases are annotated tags cut only from ra/main and never moved.
AGENTS.md, CLAUDE.md, and RUNANYWHERE.md now link to it. Docs only, nothing to build. Branch protection and making ra/main the default branch need an admin, so they're not part of this PR.