Fix .NET correctness issues from verification pass

- patterns.md: Fix cancellation pattern to use official
  TemporalException.IsCanceledException(e) with detached CancellationTokenSource
- advanced-features.md: Fix DI hosting example to use official
  AddHostedTemporalWorker(clientTargetHost:, clientNamespace:, taskQueue:) pattern

Verified against official SDK README, API docs, and temporal-docs.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

references/dotnet/advanced-features.md

@@ -118,19 +118,17 @@ The .NET SDK supports dependency injection via the `Temporalio.Extensions.Hostin
 ```csharp
 using Temporalio.Extensions.Hosting;
 
-var builder = Host.CreateApplicationBuilder(args);
-
-builder.Services.AddTemporalClient(options =>
-{
-    options.TargetHost = "localhost:7233";
-    options.Namespace = "default";
-});
-
-builder.Services.AddHostedTemporalWorker("my-task-queue")
-    .AddWorkflow<MyWorkflow>()
-    .AddScopedActivities<MyActivities>();
-
-var host = builder.Build();
+var host = Host.CreateDefaultBuilder(args)
+    .ConfigureServices(ctx =>
+        ctx.
+            AddScoped<IOrderRepository, OrderRepository>().
+            AddHostedTemporalWorker(
+                clientTargetHost: "localhost:7233",
+                clientNamespace: "default",
+                taskQueue: "my-task-queue").
+            AddScopedActivities<MyActivities>().
+            AddWorkflow<MyWorkflow>())
+    .Build();
 await host.RunAsync();
 ```
 

references/dotnet/patterns.md

@@ -345,17 +345,19 @@ public class CancellableWorkflow
                 new() { StartToCloseTimeout = TimeSpan.FromHours(1) });
             return "completed";
         }
-        catch (OperationCanceledException) when (Workflow.CancellationToken.IsCancellationRequested)
+        catch (Exception e) when (TemporalException.IsCanceledException(e))
         {
             // Workflow was cancelled — perform cleanup
-            Workflow.Logger.LogInformation("Workflow cancelled, running cleanup");
+            Workflow.Logger.LogError(e, "Cancellation occurred, performing cleanup");
+            // Use a detached cancellation token for cleanup since Workflow.CancellationToken
+            // is now cancelled
+            using var detachedCancelSource = new CancellationTokenSource();
             await Workflow.ExecuteActivityAsync(
                 (MyActivities a) => a.CleanupAsync(),
                 new()
                 {
                     StartToCloseTimeout = TimeSpan.FromMinutes(5),
-                    // Use a non-cancelled token for cleanup
-                    CancellationToken = CancellationToken.None,
+                    CancellationToken = detachedCancelSource.Token,
                 });
             throw; // Re-throw to mark workflow as cancelled
         }