electron-builder 26 dropped the app-builder-bin Go binary, so the
signed-installer staging step failed with 'node_modules/app-builder-bin/
win/x64/app-builder.exe is not recognized'. Blockmap generation now lives
in app-builder-lib's pure-JS buildBlockMap; call it through a small script
in both the release-cut and signing-rehearsal workflows.
Co-authored-by: Orca <help@stably.ai>
Neil