Refactor User Repository and API to Use Transactions

# Description

Currently, our rollback mechanism is limited to the repository layer. To ensure data consistency, we need to refactor the API and use case logic to leverage transactions effectively. This will allow rollbacks to occur not only at the repository level but also within the broader use case scope.

## Task

1. Implement Transactions in Use Case Layer

- Modify the use case to start and manage transactions.
- Ensure that a rollback occurs when an error is encountered at any step of the process.

2. Refactor User Repository

- Adapt repository methods to work within an explicit transaction context rather than managing transactions individually.
- Ensure repository methods can participate in a shared transaction.

3. Update API Layer

- Ensure the API correctly initializes transactions when calling the use case.
- Handle errors properly to trigger a rollback when necessary.