v21.7.0

• chore: fix test-lib-build script and add workspace build command
• feat: add ng-packagr build target to test-workspace test-lib for end-to-end strip verification
• fix: use direct node path for strip-showcase in test-workspace (file: link workaround)
• feat: schematic adds prism-manifest to .gitignore and logs setup summary
• docs: add library publishing guide for Showcase stripping
• feat: ng-add schematic auto-configures strip-showcase npm script
• feat: add stripShowcaseFromDirectory utility for post-build stripping
• feat: add ng-prism-strip CLI entry point
• feat: add ng-prism/transformer subpath export and ng-prism-strip bin entry
• refactor: extract isShowcaseDecorator helper to reduce duplication
• feat: implement Showcase strip transformer with 3 decorator forms
• test: add failing tests for Showcase strip transformer