Accept or Decline Applicant - API

- Validate that the user is auth and verified.
- Validate that the sent application id belongs to the logged-in user
- When user accept the offer, change the status of offer and the accepted application to "Accept" and change the status of the other applications to pending.
- Send notification to the accepted applicant with details about the accepted offer
- Return success message or error message in case of error

Start by locating the API entry point for accepting or declining an application and the existing authentication, application-status, and notification handling. Compare the implementation with each validation, status transition, notification, and success/error requirement; done means the endpoint enforces authorization and produces the specified outcomes.

Written by the indexing model from the issue text.