claudebox v2.0.11 — stop leaking a root-owned GOPATH into the full image's runtime

Dockerfile.full set GOPATH=/root/go via ENV during the Go dev-tools install
step (run as root), which leaked into the runtime container for every user.
The non-root aicode user inherited a GOPATH it doesn't own, pointing at a dir
already rm -rf'd by the same build step, so go install/get/mod failed with
permission denied. Now scoped inline to just the one RUN step; runtime falls
back to Go's own per-user default ($HOME/go).