JSON output

Add -o json to any command; MAUI/MCP/agents parse the result envelope:

{ "ok": true, "action": "vm ping", "message": "oracle reachable",
  "data": { "docker": "Docker version 29.1.3, build f52814d",
            "host": "Linux 6.12.0-105.51.5.el9uek.aarch64" } }