chore: align workflow metadata with overlay

[shiny-code-bot]

Summary

• make the workflow metadata describe local/cbusillo-overlay as the normal/default working branch
• keep fork-main documented as the upstream/fork base branch rather than the local build source of truth
• carry over the agent metadata pointer and local override ignore pattern onto the overlay

Validation

• jq empty .github/github-repo-workflow.json
• verified every metadata docs path exists
• git diff --check
• ~/.code/skills/github-repo-workflow/scripts/github-repo-snapshot.sh --json

Notes

• This PR moves the useful metadata work from the fork-main baseline onto the overlay branch where normal Code work happens.
• After this lands, GitHub's repository default branch should be changed from fork-main to local/cbusillo-overlay.