claudebox v2.0.9 — put `go` on PATH in the full image's non-login shells

The full image installed Go 1.26.1 but bare `go` only resolved in login
shells: Go's binary is in /usr/local/go/bin, which the base entrypoint's
fixed runtime PATH omits. Symlinked go+gofmt into /usr/local/bin (on that
PATH) so `go` works in the non-login agent shell too. Symlink, not move, so
GOROOT still resolves from /usr/local/go.