- Added APIKey field to Webhook model with unique index
- Implemented GenerateAPIKey() method using crypto/rand for secure key generation
- Implemented ValidateAPIKey() method to authenticate webhook requests
- Implemented RegenerateAPIKey() method to rotate API keys
- Created WebhookAPIKeyMiddleware for validating API keys in requests
- Middleware supports X-API-Key header and Authorization: Bearer format
- Added endpoint POST /api/v1/webhooks/:id/regenerate-key
- API keys are prefixed with 'whk_' for identification
- Comprehensive unit tests for all API key functionality
- Inactive webhooks cannot authenticate with their API keys
Phase: PHASE-4
Priority: P2
Progress: 119/267 (44.57%)
