[docs] Document branch protection workflow (#61)

[coisa]

Summary

• Add an advanced guide for branch protection, bot commits, wiki previews, and report previews.
• Document the wiki PR branch to master promotion lifecycle and report preview cleanup model.
• Add conflict-resolution steps for .github/wiki submodule pointer conflicts and link the guide from existing automation docs.

Verification

• git diff --check
• composer dev-tools docs

Closes #61

[github-actions]

🚀 Preview is available for this pull request.

• Docs: https://php-fast-forward.github.io/dev-tools/previews/pr-77/
• Coverage: https://php-fast-forward.github.io/dev-tools/previews/pr-77/coverage/