dead-letter-queues: refresh for Track 2 SDK + drop stale references (#317117)
- Path to the DLQ: replace Track 1 `QueueClient.FormatDeadLetterPath` /
`SubscriptionClient.FormatDeadLetterPath` snippet (no Track 2 equivalent
exists - the path is abstracted behind `SubQueue.DeadLetter`) with prose
that points Track 2 readers to the new receive example.
- Add new "Receive messages from a dead-letter queue" section with a
runtime-verified `Azure.Messaging.ServiceBus` snippet showing
`SubQueue.DeadLetter`, `DefaultAzureCredential` passwordless auth,
inspection of `DeadLetterReason` / `DeadLetterErrorDescription`, and
`CompleteMessageAsync`. Mentions `SubQueue.TransferDeadLetter` for TDLQ.
- Sending dead-lettered messages: drop the StackOverflow link and the
third-party "Available tools" bullet list (ServicePulse with NServiceBus,
ServicePulse with MassTransit); keep Service Bus Explorer guidance in
prose linking to the new explorer.md#resend-a-message anchor.
- Verified no other Track 1 (`Microsoft.Azure.ServiceBus`) SDK residue
remains in the article.
Snippet verified end-to-end against Azure.Messaging.ServiceBus 7.20.1 +
Azure.Identity 1.13.1 on .NET 10 against a live Standard-tier namespace
on 2026-06-15.
Co-authored-by: Eldert Grootenboer (from Dev Box) <egrootenboer@microsoft.com>