Updated RecentReceiverSuggestionDto to use `init` properties,
adding immutability and a new `LastUsedAt` field. Refactored
ReadRecentReceiverSuggestionsQueryHandler to simplify query
logic, remove `IMapper` dependency, and improve determinism
in results. Introduced tie-breaking for duplicate timestamps
and optimized ordering by `LastUsedAt` and `EmailAddress`.
Removed redundant `Include` and mapping steps for clarity.
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`.
