Adds a webui service to docker-compose that wraps Claude Code in ttyd,
serving a browser-accessible terminal on port 7681. The webui reuses
Dockerfile.claude (ttyd added to apt deps) with a dedicated entrypoint
script that enforces WEBUI_PASSWORD before starting. Network isolation
is identical to the CLI container: claude-internal only, all egress via
the proxy allowlist. claude.sh gains web and web-stop commands.
