Register a new agent

curl --request POST \
  --url https://app.mandate.md/api/agents/register \
  --header 'Content-Type: application/json' \
  --data '
{
  "name": "Treasury Bot",
  "evmAddress": "0x71C7656EC7ab88b098defB751B7401B5f6d8976F",
  "chainId": 84532,
  "defaultPolicy": {
    "spendLimitPerTxUsd": 100,
    "spendLimitPerDayUsd": 1000
  }
}
'

{
  "agentId": "9e5f1a2b-3c4d-5e6f-7a8b-9c0d1e2f3a4b",
  "runtimeKey": "mndt_test_abc123def456ghi789jkl012mno345",
  "claimUrl": "https://app.mandate.md/claim?code=A1B2C3D4",
  "walletAddress": "0x71c7656ec7ab88b098defb751b7401b5f6d8976f",
  "evmAddress": "0x71c7656ec7ab88b098defb751b7401b5f6d8976f",
  "chainId": "84532",
  "defaultPolicy": {
    "spendLimitPerTxUsd": 100,
    "spendLimitPerDayUsd": 1000
  }
}