Parent-wins propagation

All pipeline operators copy the incoming result's Context to the outgoing result. The child result's context is ignored — the pipeline entry point's context flows through to the end:

var result = Result<Order>.Ok(order)
    .WithContext(entityId: "42", correlationId: "trace-1")
    .Bind(ValidateStock)          // child result context ignored — parent wins
    .Bind(ProcessPayment)
    .Map(o => new OrderDto(o));   // Entity updated to "OrderDto", all other fields preserved

// result.Context.EntityId      = "42"       ← from original WithContext
// result.Context.CorrelationId = "trace-1"  ← from original WithContext
// result.Context.Entity        = "OrderDto" ← Map updates Entity to typeof(TOut).Name