Read org security metrics (overview / health / timeline / posture).

Returns security dashboard metrics scoped to the authenticated org. `metricType` selects the projection: overview (all sections), health, timeline, or posture. `timeRange` ∈ 24h/7d/30d/90d. Bearer-reachable for human principals (user token or browser session); rsk_* API keys and BYOA OAuth-agent tokens are rejected 403.

curl -X GET "https://example.com/api/security/metrics"

{
  "metrics": {
    "property1": null,
    "property2": null
  },
  "health": {
    "property1": null,
    "property2": null
  },
  "timeline": [
    {
      "property1": null,
      "property2": null
    }
  ],
  "posture": {
    "property1": null,
    "property2": null
  },
  "actorNames": {
    "property1": "string",
    "property2": "string"
  }
}