Add the response field to webhook delivery attempt types #256

Problem

The API contract requires a response field on webhook delivery attempts: ProjectWebhookDeliveryAttempt and OrganizationWebhookDeliveryAttempt in the Management spec at API 1600403db9dcf7996dbbb882375b1165859829d3. The TypeScript SDK's WebhookDeliveryAttemptBase (packages/typescript/src/platform/developer-types.ts) doesn't declare it.

As a result, consumers can't read the response excerpt through a typed field. polymorfa/cli#3 works around this by reading the field defensively.

Expected

• Add response with the exact shape and nullability from the spec snapshot.
• Extend the compile-time contract shape check so this field can't drift again.
• Update the README if it documents delivery attempts.
• After this merges, remove the defensive read in the CLI (Add developer workflows, local listener, and MCP cli#3).