chore: migrate to Policyfile

[damacus]

Summary

• replace Berksfile/Berkshelf usage with Policyfile resolution
• switch Kitchen to policyfile_zero and map Windows suites to Policyfile named run lists
• update Copilot setup to install cookbooks with chef install Policyfile.rb

Verification

• chef install Policyfile.rb
• cookstyle --no-server --cache-root /private/tmp/rubocop_cache
• /opt/homebrew/bin/markdownlint-cli2 "**/*.md"
• env GEM_HOME=/opt/chef-workstation/embedded/lib/ruby/gems/3.1.0 GEM_PATH=/opt/chef-workstation/embedded/lib/ruby/gems/3.1.0 GEM_PATH_SYSTEM= /opt/chef-workstation/embedded/bin/rspec --format documentation
• env -u KITCHEN_LOCAL_YAML kitchen list
• env -u KITCHEN_LOCAL_YAML kitchen diagnose vc6-windows-2019

Kitchen note: meaningful suites are Windows Vagrant/WinRM targets, so local Linux Kitchen smoke was intentionally not run.