Fix VERSION not included in Nix package and Makefile bundle

- flake.nix: copy VERSION file to $out/ so josh_sync_version() finds it
- Makefile: add lib/onboard.sh to the bundle loop

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

flake.nix

@@ -28,6 +28,7 @@
 
             installPhase = ''
               mkdir -p $out/{bin,lib}
+              cp VERSION $out/
               cp lib/*.sh $out/lib/
               cp bin/josh-sync $out/bin/
               chmod +x $out/bin/josh-sync