Refactor: Rename OutgoingEmail to SendingEmail

This commit renames and refactors all instances of `OutgoingEmail` to `SendingEmail` across the codebase to improve terminology consistency and align with domain language.

- Renamed classes, interfaces, and records (e.g., `OutgoingEmailPublisher` → `SendingEmailPublisher`, `OutgoingEmailEvent` → `SendingEmailEvent`).
- Updated method signatures, parameters, and return types to use `SendingEmail`.
- Adjusted dependency injection registrations to reflect the new naming.
- Updated mappings in `EmailMappingProfile` to map `SendEmailCommand` to `SendingEmailEvent`.
- Refactored `SendEmailCommand` and its handler to work with `SendingEmailEvent`.
- Updated `EmailsController` to use `SendingEmailEvent` in the `SendEmail` action.
- Refactored integration tests to test `SendingEmailPublisher` and updated test data accordingly.
- Updated log messages, error handling, and comments to reflect the new terminology.
- Revised documentation and utility methods to use `SendingEmailEvent`.

This refactor ensures consistency, improves readability, and reduces ambiguity in the codebase.

src/presentation/DigitalData.MessagingService.Client/EmailSender.cs

@@ -113,8 +113,8 @@ public static class EmailSender
     /// Thrown when <see cref="ConnectRabbitMq(Action{RabbitMqConfiguration}, OnReconnect)"/> has not been called prior to sending.
     /// </exception>
     /// <remarks>
-    /// This method maps <see cref="Email"/> to <see cref="OutgoingEmailEvent"/>,
-    /// then resolves <see cref="IOutgoingEmailPublisher"/> from the internal
+    /// This method maps <see cref="Email"/> to <see cref="SendingEmailEvent"/>,
+    /// then resolves <see cref="ISendingEmailPublisher"/> from the internal
     /// service provider and calls <c>EnqueueAsync</c> in a fire-and-forget manner.
     /// Ensure that any unhandled exceptions from the async operation are handled
     /// at the publisher level.
@@ -124,7 +124,7 @@ public static class EmailSender
         if(!IsConnected)
             throw new InvalidOperationException("Messaging service is not connected. Call ConnectRabbitMq first.");
 
-        var publisher = LazyProvider.Value.GetRequiredService<IOutgoingEmailPublisher>();
+        var publisher = LazyProvider.Value.GetRequiredService<ISendingEmailPublisher>();
         publisher.EnqueueAsync(email.ToEvent());
     }
 }