fix(github): allow redelivery and re-processing of failed webhooks (#317)

[Proxima84-code]

Resolves #317.

Summary of Changes

• Controller: Throws InternalServerErrorException (HTTP 500) when webhook processing status is FAILED, prompting GitHub to schedule an automatic redelivery.
• Service: Intercepts redeliveries matching an existing deliveryId in FAILED status, resets status to RECEIVED (error and processedAt to null), and re-executes business logic instead of dropping the event as a duplicate.
• Unit Tests:
  • Added test case verifying HTTP 500 response on failed event processing in controller.
  • Added test case verifying business logic re-execution for retry deliveries in service.
  • Fixed mock definitions across webhook test suites.

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