SSH access to TrueNAS covers all Docker management needs (docker compose,
logs, restarts) making a dedicated Docker MCP redundant.
- Add ssh-mcp (port 8600): execute shell commands, read files, list dirs,
tail logs, find files, check disk usage on the TrueNAS host via asyncssh
- Remove docker-mcp (port 9000): redundant given SSH access to the host
- Update docker-compose.yml: wire in ssh-mcp service, remove docker-mcp
service and its MCP_BACKEND_DOCKER gateway env var
