Gets the budget configuration for an agent, including current cost and usage data

Returns the budget cap, period, alert thresholds, and the live cost accumulated against the current period (sourced from the same execution-cost stream that powers `GET /v1/tenants/{tenant}/agents/{agent}/revisions/{revision}/cost`). A 404 here means the agent has no budget enforcement and runs are uncapped — it does not mean the agent itself is missing. Use this to drive budget UI and to check headroom before kicking off expensive batches.

curl -X GET "https://api.fruxon.com/v1/tenants/string/agents/string/budget"

{
  "agentId": "string",
  "amount": 0,
  "thresholdRules": [
    {
      "percent": 0
    }
  ],
  "enforceLimit": false,
  "currentMonthlyCost": 0,
  "usagePercent": 0,
  "periodStart": 0,
  "periodEnd": 0,
  "createdAt": 0,
  "modifiedAt": 0
}