fix: migrate to Policyfile and repair ci final job

[damacus]

Summary

• Replace Berksfile dependency resolution with Policyfile.rb
• Update ChefSpec and Kitchen to use Policyfile resolution
• Update Copilot setup to run chef install Policyfile.rb

Verification

• chef install Policyfile.rb
• cookstyle --no-server --cache-root /private/tmp/rubocop_cache
• markdownlint-cli2 "**/*.md"
• embedded rspec --format progress
• git diff --check

[github-actions]

Slowest examples

Top 3 slowest examples (0.1 seconds, 100% of total time)

Example	Description	Time in seconds
spec/unit/recipes/default_spec.rb:6	default recipe on Windows 2012 R2 converges successfully	0.04347
spec/unit/recipes/default_spec.rb:26	webpi::install-zip extracts the downloaded WebPI command line archive	0.04158
spec/unit/recipes/default_spec.rb:14	default recipe on Windows 2016 converges successfully	0.01607