docs(cloud): Add Deploy from CI with GitHub Actions guide and retitle Redis guide

[developerjamiu]

PR 7 of the Cloud IA rollout (#568). Establishes the Guides section.

Summary

• New guide: Deploy from CI with GitHub Actions at `/cloud/guides/deploy-from-ci-with-github-actions`. Reframes the old `reference/01-deployment/06-github-automation` page as a how-to. Includes a primary workflow (committed generated code, simplest path), a variant workflow (generate in CI), an action inputs reference table, and troubleshooting tied to failures readers actually hit. Validated end-to-end on a test repo: primary path deploys successfully when `scloud.yaml` is committed at the repo root.
• Redis guide retitle and template alignment: "Redis (PubSub and caching)" → "Use Redis for PubSub and caching". Adds a description frontmatter line, renames `Prerequisites` → `Before you start`, and reformats `Related` bullets to match the Ship-non-Dart-files guide pattern from PR 5. No content rewrites.
• Cross-doc updates: the PAT concept's GitHub Actions section now links to the new guide instead of the external action README. The Deployments concept's Related entry repoints to the new guide URL. A redirect from `/cloud/reference/deployment/github-automation` to the new guide URL is added.

Test plan

• `npm run build` passes in CI.
• Redirect from `/cloud/reference/deployment/github-automation` resolves to the new guide URL.
• The PAT concept's GitHub Actions section now links inward.
• The new guide's primary workflow deploys an end-to-end test project (validated locally by author).