Test: subc format goldens accept the home-relative project root
Three subc_format_test goldens always failed on our build servers and passed on GitHub runners. The renderer abbreviates paths under HOME to ~/..., and the build servers keep the scratch project under HOME=/motor-home, so rendered paths read ~/... while the comparison only replaced the absolute project root.
The comparison helper now also replaces the ~-spelling of this project root. It leaves unrelated home-relative paths in a golden untouched, and a unit test pins both cases. Test-only; no product code changes.
On the build server (HOME=/motor-home): all 11 subc_format_test tests pass, with formatting checked.
Summary by cubic
Fixes subc_format_test goldens that failed on build servers because the renderer abbreviates paths under HOME to ~/.... The comparison helper now normalizes both the absolute and ~-relative spellings of the project root, leaving unrelated home-relative paths untouched. Test-only change.