Brightencode Launcher v0.1.24

Fall back to sha256sum when shasum isn't on PATH

Windows' Git Bash runner apparently dropped shasum (Perl-based) from its
default PATH — v0.1.24's Windows release build failed at the
beforeBuildCommand step with "shasum: command not found", even though
v0.1.23 built fine 5 days earlier. sha256sum (GNU coreutils) reads the same
checksum-file format and is available on Linux/Windows; shasum stays as
the fallback for macOS, which doesn't ship sha256sum by default.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>