Replaced `IMailRepository` with `IReceivedEmailRepository` to improve modularity and functionality. Updated `IReceivedEmailRepository` to make the `EmailAccount` parameter optional in the `FindAsync` method.
Added `ReceivedEmailRepository` with advanced filtering capabilities, including account, flags, text, UID, date, and recipient filters. Implemented deferred materialization for recipient filtering due to EF Core limitations.
Registered `IReceivedEmailRepository` in dependency injection. Updated `ReadEmailQueryHandler` to use the new repository. Improved query performance by applying filters conditionally.
