Excess Worker 0.2.1

Release sequence 28. Anonymous Minisign release signing. Windows executables have no trusted Authenticode publisher signature.

Linux 0.2.0 installations: excess-worker update in 0.2.0 refuses this package because the 0.2.0 updater accepts only the earlier GPU helper profile; it leaves 0.2.0 unchanged. Drain the worker, verify the downloaded files, then run the 0.2.1 install.sh over the same install location. Windows 0.2.0 installations update with excess-worker update. See docs/INSTALLATION.md ("Stop, revoke and update").