WAMP-cryptosign: support Putty/Pageant (Windows)

WAMP-cryptosign can (optionally) use OpenSSH ssh-agent on Unix systems. Most Windows users are nowerdays probably using Putty and Pageant. The latter uses a weird, shared-memory mapped file for communication. Seems undocumented also. A couple of projects have reverse engineered this stuff:

• https://github.com/paramiko/paramiko/blob/master/paramiko/win_pageant.py
• https://github.com/Yasushi/putty/blob/master/windows/winpgntc.c#L155
• https://github.com/ymnk/jsch-agent-proxy/blob/master/jsch-agent-proxy-pageant/src/main/java/com/jcraft/jsch/agentproxy/connector/PageantConnector.java

"Best I understand, the protocol is the same, but the transport is different, using shared memory rather than sockets."

I am mainly filing this issue to point users to. We have NO plans to support Putty/Pageant on Windows for WAMP-cryptosign. Sorry guys. Move along, nothing to see here;)

IOW: won't fix!

But note: WAMP-cryptosign can be used on Windows - but only by directly accessing the private key (either raw or OpenSSH format). It's just that Pageant is not supported.

This issue is explicitly a won't-fix reference for Pageant support, with no repository files or tests identified. The linked Paramiko, PuTTY, and JSch implementations are the available research starting points, but there is no defined completion target because the project has no plans to implement the feature.