assets/creator-studio/build is generated by `npm run build`, so committing it
put a rebuilt bundle in every diff. It now follows the same deploy-only rule
as assets/admin/build.
- Root .gitignore ignores build/* and node_modules/, keeping a .gitkeep so
the directory still exists in a clean checkout.
- Drops the three tracked artifacts from the index.
- The contract test no longer requires the artifacts to exist; it checks the
set is all-or-nothing, so a clean checkout and a locally built tree both
pass. This mirrors admin-build-graph-contract.
- README documents that build/ is produced on the target machine.
887 widget-system tests pass.
kate522
