GET Usage billing enrichi

GET /api/v1/billing/usage

{
  "data": {
    "plan": {
      "code": "pro",
      "name": "Pro"
    },
    "limits": {
      "maxInstances": 5,
      "maxApiKeys": 5,
      "maxWebhookEndpoints": 10,
      "monthlyOutboundQuota": 25000,
      "monthlyApiRequestQuota": 100000
    },
    "features": {
      "campaigns": true,
      "statuses": true,
      "voiceNotes": true,
      "webhooks": true
    },
    "usage": {
      "messagesCount": 1240,
      "statusesCount": 85,
      "effectiveOutboundUsage": 1325,
      "apiRequestsCount": 4500,
      "activeInstancesCount": 3,
      "activeApiKeysCount": 2
    },
    "period": {
      "start": "2026-04-01T00:00:00.000Z",
      "end": "2026-04-30T23:59:59.999Z"
    }
  }
}