Introduce `RecentReceiverSuggestionDto` to represent recent receiver suggestions with `FullName` and `EmailAddress`.
Add `ReadRecentReceiverSuggestionsQuery` to retrieve recent receiver suggestions scoped by sender username and limited to 3-5 results.
Implement `ReadRecentReceiverSuggestionsQueryHandler` to process the query using Entity Framework Core and AutoMapper.
Update `MappingProfile` to map `EnvelopeReceiver` to `RecentReceiverSuggestionDto`.
