Purchase Add-on

curl -X POST "https://app.crovver.com/api/public/tenants/workspace_123/addons/purchase" \
  -H "Authorization: Bearer sk_live_..." \
  -H "Content-Type: application/json" \
  -d '{
    "addonId": "uuid",
    "currency": "USD",
    "idempotencyKey": "addon-purchase-1778423112701",
    "successUrl": "https://app.com/settings?addon=purchased",
    "cancelUrl": "https://app.com/settings"
  }'

{
  "success": true,
  "data": {
    "purchaseId": "uuid",
    "checkoutUrl": "https://checkout.stripe.com/pay/cs_...",
    "requiresPayment": true,
    "addonName": "API Call Pack",
    "creditQty": 500,
    "amount": 5,
    "currency": "USD"
  }
}

{
  "success": true,
  "data": {
    "purchaseId": "uuid",
    "checkoutUrl": "https://checkout.stripe.com/pay/cs_...",
    "alreadyProcessed": true
  }
}

{
  "success": false,
  "error": "Currency mismatch: subscription uses NPR"
}