The SPA (web/) and the web gateway (cmd/webgw) move to a dedicated app
projects/message_bus/apps/uniweb (its own Gitea sub-repo). unibus is now
strictly the bus plane: membership/keys, the client library and demo peers.
uniweb consumes unibus as a Go module via replace => ../unibus.
No capability lost; same SPA and gateway, in their own service folder.
go build/vet/test green after extraction.
