Client Onboarding

Partner ──POST /v2/onboard──> API ──> Validate Partner is Active
                                  ──> Create Company + default organization unit (business_entity)
                                  ──> Generate Company API Key
       <── 200 OK ──────────── API
           { companyId, organizationUnitId, companyApiKey, message }

{
  "name": "Acme Corporation",
  "legalName": "Acme Corp Ltd.",
  "country": "US",
  "taxId": "123-456-789",
  "phone": "+1234567890",
  "address": "123 Main St",
  "postalCode": "10001",
  "city": "New York"
}

{
  "companyId": "01HXYZ...",
  "organizationUnitId": "01HXYZ...",
  "companyApiKey": "eve_ck_...",
  "message": "Company onboarded successfully"
}