`resendVerificationOtp` wraps all errors in `InternalServerErrorException`, hiding meaningful 4xx errors

[Nabeelahh]

Area: Backend

• Description: The top-level catch in resendVerificationOtp re-throws every exception (including BadRequestException and NotFoundException) as a 500 InternalServerErrorException. The original status code and message are lost, making it impossible for clients to distinguish a missing email from a server crash.
• File(s): backend/src/auth/auth.service.ts
• Priority: Medium
• Implementation & verification: Trace all controller, service, provider, and module-registration callers before changing the implementation so the DTO and HTTP-error contract remains stable. Add focused automated coverage for the reported failure mode and the expected successful path, mocking external services where applicable.