AJ ONeal 76fbf74444
fix(monorel): error if binary path is not a main package
Add checkPackageMain(), which uses go/parser with PackageClauseOnly mode
(reads only the package-declaration token of each .go file — very fast)
to verify the resolved binary directory declares `package main`.

Called in groupByModule for every argument after resolving the absolute
path, before findModuleRoot.  Produces a helpful error, e.g.:

  monorel: error: .../io/transform/gsheet2csv is package "gsheet2csv",
                  not a main package
2026-03-01 19:13:49 -07:00
..