GET Lister les groupes

GET /api/v1/contacts/groups

{
  "data": {
    "groups": [
      {
        "id": "grp_uuid",
        "name": "VIPs",
        "description": "Contacts prioritaires",
        "color": "#facc15",
        "contactCount": 42,
        "createdAt": "2026-04-01T10:00:00.000Z"
      }
    ],
    "total": 7,
    "limit": 50,
    "nextCursor": null,
    "hasMore": false
  }
}