feat(mediator): generate Rebus owner routing

[Copilot]

Implements the next planned mediator-framework task, T11.4: generate Rebus owner routing from message contracts instead of maintaining manual type maps.

• Contract metadata

  • Add optional OwnerQueue to RebusMessageAttribute.
  • Validate blank queues and conflicting declarations via generator diagnostics.

• Generated routing

  • Emit ConfigureArkRebusRouting.
  • Register owned messages through Rebus TypeBased().Map<TMessage>(queue) routing.

[RebusMessage(OwnerQueue = "ark.mediator.sample")]
public sealed record CompleteGreetingCompositionRequest
    : IRequest<GreetingResponse>;

• Sample and documentation
  • Wire the sample composition root to generated routing.
  • Add generator coverage for routing, invalid queues, and conflicts.
  • Update the mediator implementation plan and task order.

[AndreaCuneo]

RebusMessage cannot be applied multiple times Owner Queue must be unique unique

[AndreaCuneo]

@copilot resolve open comments

[Copilot]

@copilot resolve open comments

Resolved in commit f01c5fb: RebusMessageAttribute now allows only one declaration, and generator conflict handling/tests were removed accordingly. Targeted and full solution tests pass.