Set up the relay workflow

Set up, update, or adopt the relay workflow in a repository, the planner/executor process run by relay-project, relay-next, relay-execute, and relay-release. Builds on the repo's instruction baseline from instructions-setup (running it first when missing), then writes the "Relay workflow" section of AGENTS.md (branches, gate command, CI, how releases and GitHub Issues fit in, authority docs, file paths) and scaffolds the status file, chunk directory, review and brief checklists, and project registry. Use when the user wants to start working in chunks, set up the planner/executor or relay workflow, "set up relay", adopt the relay skills in a repo, migrate a repo's own plan…