go build inside the Docker image runs outside the workspace, so server/go.sum
needed the hyperboloide/lk entry that GOWORK resolution was supplying locally.
Caught by the image build, not by go build.
Also pins the explicit shared require in both go.mod files. `go mod tidy`
in workspace mode drops it, which breaks the Docker build where no
workspace exists.
mrhid6
domrichardson