Check accounts health

{
  "summary": {
    "total": 5,
    "healthy": 3,
    "warning": 1,
    "error": 1,
    "needsReconnect": 1
  },
  "accounts": [
    {
      "accountId": "abc123",
      "platform": "instagram",
      "username": "myaccount",
      "status": "healthy",
      "canPost": true,
      "canFetchAnalytics": true,
      "tokenValid": true,
      "tokenExpiresAt": "2025-06-15T00:00:00Z",
      "needsReconnect": false,
      "issues": []
    },
    {
      "accountId": "def456",
      "platform": "twitter",
      "username": "mytwitter",
      "status": "error",
      "canPost": false,
      "canFetchAnalytics": false,
      "tokenValid": false,
      "needsReconnect": true,
      "issues": [
        "Token expired"
      ]
    }
  ]
}

{
  "error": "Unauthorized"
}