INT-904: Modernize generated Homebrew install steps

[rianjs]

[INT-904]

Summary

• normalize GoReleaser's deprecated preflight/postflight block names before publishing casks
• translate legacy system_command calls and staged-path interpolation to Homebrew's install-step DSL
• derive canonical and alias casks from the same normalized file
• add portable regression and idempotence tests

Verification

• bash actions/homebrew-alias/test_modernize.sh
• bash actions/homebrew-alias/test_alias.sh
• real GoReleaser snapshot casks from cpm, hubspot-cli, and salesforce-cli normalize successfully
• Homebrew Cask/InstallSteps style check passes on those real outputs

Rollout

After merge, advance the movable v1 tag to the merge commit before merging the dependent legacy publisher PRs.