feat: expose RabbitMQ delivery context

Add backward-compatible context-aware handling and permanent validation hooks.

Ref: IT-1033

Hrynco.RabbitMq/README.md

@@ -6,10 +6,22 @@ RabbitMQ publisher and consumer base for HrynCo applications.
 
 - `RabbitMqSettings` — connection settings record (host, port, user, password, virtual host)
 - `IRabbitMqPublisher` / `RabbitMqPublisher` — publishes JSON-serialized messages to a named queue
-- `RabbitMqConsumerBase<TMessage, TMessageData>` — abstract background service base for consumers, with retry + dead-letter support
+- `RabbitMqConsumerBase<TMessage, TMessageData>` — background service base with connection management, manual ACK/NACK, retry, permanent-validation rejection, and backward-compatible context-aware handling
+- `RabbitMqMessageContext` — neutral AMQP delivery metadata (`MessageId`, type, correlation, routing, headers, and redelivery state)
 - `IRabbitMqMessage<TMessageData>` — message contract interface
 - `CorrelationContext` — correlation ID carrier
 
 ## Packaging
 
 This package is intended for reuse through NuGet. The test project is excluded from packing.
+
+## Consumer extension points
+
+Existing consumers can keep overriding `HandleMessageAsync(message, cancellationToken)`.
+Consumers that need AMQP metadata can instead override
+`HandleMessageAsync(message, context, cancellationToken)`. The base class retains
+ownership of acknowledgements and retries.
+
+Override `TryValidateMessage(...)` for application-specific permanent validation.
+Returning `false` nacks the delivery without requeue before retry processing begins.
+Keep validation errors free of credentials and sensitive payload values.