Adds transactional outbox and email verification

Implements outbox pattern for reliable message delivery
Adds email verification flow with Postmark integration
Enhances account registration with secure token generation

Introduces background processing for asynchronous email sending
Implements database-level notification mechanism for message processing

Core/Database/SqlOperations.cs

@@ -19,6 +19,7 @@ public class SqlOperations : IDatabaseOperations
     public DatabaseScope CreateScope(string operationName)
     {
         var connection = _connectionFactory.Create();
+        connection.Open();
         var operation = _telemetryClient.StartOperation<DependencyTelemetry>(operationName);
         operation.Telemetry.Type = "SQL";
         operation.Telemetry.Target = "PostgreSQL";