Rectangles and Irregular now ship inside OpenNest.Engine.dll, so the Windows
package no longer fetches, tests and bundles OpenNest-Engines at a pinned
commit. Removes scripts/external-engines.json and the Engines/ folder,
manifest and license from the package; build-info.json drops enginesCommit.
ReleaseSmoke now checks the packaged registry: every built-in engine must
instantiate from the packaged OpenNest.Engine.dll, the Opus55NestingEngine
name must resolve to Irregular, and an unknown name must be rejected. Linux
check against a published OpenNest.Engine: pass case exit 0; missing engine
DLL exit 1. Full Windows packaging still needs the Windows runner.
aj