The C# ServUO plugin (overlay/, patches/, deploy.ps1, tools/) has been
extracted with full history via git filter-repo into the new
RunicGateway/servuo-plugins repo. This repo is now the Rust sidecar only.
Rewrite the README to be sidecar-focused: related-repos table, build/run,
and a deployment/compatibility section describing the runtime protocol
relationship with the plugin. No source cross-references existed between the
two halves, so nothing else needed repointing.
Plugin repo: https://gitea.whitlocktech.com/RunicGateway/servuo-plugins
