feat: Add transaction confirmation dialog

[Creative-Titilayo]

Overview

This PR adds a webhook event dispatch system to apps/api so merchant systems can be notified when payment lifecycle events occur. It introduces support for payment.created, payment.detected, payment.confirmed, and payment.failed, and sends a standardized JSON payload containing the event type, data object, and timestamp.

Related Issue

Closes #15

Changes

⚙️ Webhook Dispatch System

• [ADD] apps/api/src/webhooks/webhooks.service.ts

• Added the core webhook dispatch service for payment lifecycle events.

• Implemented support for payment.created, payment.detected, payment.confirmed, and payment.failed.

• Standardized the payload format to include event, data, and timestamp.

• Added JSON POST delivery with a configurable timeout.

• Added optional HMAC SHA-256 signing for webhook endpoints with a shared secret.

• [ADD] apps/api/src/webhooks/interfaces/webhook-event.interface.ts

• Defined the supported webhook event types.

• Added shared interfaces for webhook payloads, endpoints, and delivery results.

• [ADD] apps/api/src/webhooks/interfaces/dispatch-webhook.interface.ts

• Added request and response interfaces for webhook dispatch operations.

🌐 Webhook API Surface

• [ADD] apps/api/src/webhooks/webhooks.controller.ts

• Added a public POST /webhooks/dispatch endpoint to trigger webhook dispatch.

• Accepts a standardized event, payload data, and one or more target endpoints.

• [ADD] apps/api/src/webhooks/webhooks.module.ts

• Added a dedicated NestJS module for webhook dispatch.

• Exported the webhook service for reuse by future payment lifecycle code.

• [MODIFY] apps/api/src/app.module.ts

• Registered the new WebhooksModule in the API app.

🧪 Tests

• [ADD] apps/api/src/webhooks/webhooks.service.spec.ts
• Added tests for standardized payload creation.
• Added tests for signature generation.
• Added tests for webhook delivery behavior.
• Added validation coverage for empty endpoint lists.

🔧 Configuration

• [MODIFY] apps/api/.env.example
• Added WEBHOOK_TIMEOUT_MS to configure webhook request timeouts.

Verification Results

Acceptance Criteria	Status
Supports payment.created event	✅
Supports payment.detected event	✅
Supports payment.confirmed event	✅
Supports payment.failed event	✅
Payload includes event, data, and timestamp	✅
Webhook dispatch logic is implemented in the API	✅
API build passes successfully	✅
Webhook service tests pass successfully	✅

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