Normalize repo-backed guest checkouts to /root/repo so vm run, attach, and
follow-on guest tooling stop depending on the source repository name.
Add `banger vm acp [--cwd] <vm>` as an SSH stdio bridge to guest `opencode acp`,
defaulting to /root/repo when that checkout exists and falling back to /root.
Update the README and CLI coverage around the fixed guest path and ACP command.
Validation: go test ./internal/cli, go test ./..., make build.
Thales Maciel
5f89c07fc0