v0.0.4: build: register macOS native content items after BuildBinMac runs

BuildBinMac with BeforeTargets=Build runs *after* CoreBuild (the Build
target body is empty; its dependencies execute first), so the cmake
outputs didn't exist yet when the static <Content Include> items tried
to copy.  Locally this masked itself behind leftover artifacts from
prior runs; on a clean CI checkout the copy step failed.

Move BuildBinMac to BeforeTargets=AssignTargetPaths and register the
dylib/helper/plist as Content items inside the same target, so the
items only materialise once the files are on disk.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>