Declare transformed plugin archive coverage for releases #1829

Problem

WP Codebox packages packages/wordpress-plugin/** under the transformed ZIP root wp-codebox/**. Homeboy now supports generic per-artifact source-root to archive-root completeness mappings through Extra-Chill/homeboy#8499, but WP Codebox must declare its intended layout before the interrupted v0.12.23 release can pass fail-closed package validation.

The prior release attempt passed build, smoke tests, versioning, and release commit creation, then correctly stopped before tag/push/publication because literal repo-relative completeness could not represent the transformed plugin ZIP. No remote release state was created.

Acceptance

• homeboy.json declares the plugin ZIP artifact, source root packages/wordpress-plugin, and archive root wp-codebox.
• The declaration uses exact artifact matching.
• Repository contract coverage validates the generic declaration and package layout.
• The plugin ZIP contains every mapped tracked runtime file required by the declaration.
• CLI tarball packaging remains unchanged.
• The repaired Homeboy release preflight accepts the generated artifacts without skipped checks.

Related: #1822, #1823, Extra-Chill/homeboy#8499, Extra-Chill/homeboy#8524.