Duplicate verification error message fix.

[5eeman]

Added correct error message for a case when verification request was already verified.

[Copilot]

Pull Request Overview

Adds handling for cases where a verification request has already been processed, logging an error and returning an error response.

• Introduces a type check for models.VerificationResponse to detect duplicate verifications
• Logs an error and returns a 500-style JSON response with message "request already verified"

Comments suppressed due to low confidence (2)

internal/api/server.go:101

• Using a 500 Internal Server Error for an already verified request may mislead clients; consider returning a 409 Conflict or 400 Bad Request with an appropriate response type to reflect a client-side issue.

		return Callback500JSONResponse{

internal/api/server.go:96

• There is no existing test coverage for the duplicate verification path; add a unit or integration test to ensure this branch behaves as expected.

	// Check if request is already verified