ci(guardrails): protect the guardrails-release branch and tag name with rulesets #9531

Refs: #9504

Problem

After #9504, every consumer repository's lefthook remotes: entry fetches the guardrails git hooks from this repository's guardrails-release ref and runs them on developer machines, refetching every 24h. Only .github/workflows/release-move-guardrails-ref.yml should move that ref, but today nothing enforces it:

• Any account or workflow token with contents: write can push, force-push or delete refs/heads/guardrails-release. The workflow's "Refuse any ref but main" step lives in a file a non-main branch can edit, so a branch workflow with a write token is enough.
• lefthook fetches ref by its short name (git fetch --depth 1 origin -- <ref>, lefthook v2.2.2 internal/git/wrapper/fetch.go), and git resolves a short name to refs/tags/<name> before refs/heads/<name>. A tag named guardrails-release therefore replaces the branch for every consumer. A full refs/heads/... ref cannot be used, because lefthook's initial clone --branch rejects it. feat(guardrails): serve the git hooks to lefthook repositories as a remote #9504's workflow now refuses to move the branch while such a tag exists, but that only detects it at release time.
• Deleting the branch and re-dispatching the workflow recreates it at any commit on main, including an older release.

Today the repository's rulesets cover only the default branch and refs/heads/release/plugins (gh api repos/melodic-software/claude-code-plugins/rulesets).

Proposed fix (melodic-software/github-iac)

1. A branch ruleset on refs/heads/guardrails-release: restrict creation, update and deletion, and block non-fast-forward.
2. A tag ruleset blocking creation of refs/tags/guardrails-release (or refs/tags/guardrails-*).
3. A bypass for the move workflow only. Use a dedicated GitHub App whose key is in an environment limited to main, and have the workflow mint that app's token, as release-plugins does with its own Integration. Do not use the GitHub Actions app, because that would give every workflow the bypass. The workflow's GITHUB_TOKEN push then changes to the app token.

Acceptance

• A push to, a deletion of, or a non-fast-forward of guardrails-release from any actor other than the move workflow is rejected.
• Creating the tag guardrails-release is rejected.
• The move workflow still creates and moves the branch.