perf(router): replace 100ms Valkey polling with Pub/Sub notification wakeup and increase heartbeat to 45s

The Valkey transport layer used 100ms busy-polling loops (Task.Delay(100))
across ~90 concurrent loops in 45+ services, generating ~900 idle
commands/sec and burning ~58% CPU while the system was completely idle.

Replace polling with Redis Pub/Sub notifications:
- Publishers fire PUBLISH after each XADD (fire-and-forget)
- Consumers SUBSCRIBE and wait on SemaphoreSlim with 30s fallback timeout
- Applies to both ValkeyMessageQueue (INotifiableQueue) and ValkeyEventStream
- Non-Valkey transports fall back to 1s polling via QueueWaitExtensions

Increase heartbeat interval from 10s to 45s across all transport options,
with corresponding health threshold adjustments (stale: 135s, degraded: 90s).

Expected idle CPU reduction: ~58% → ~3-5%.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

src/Router/__Tests/StellaOps.Router.AspNet.Tests/StellaRouterOptionsTests.cs

@@ -41,7 +41,7 @@ public sealed class StellaRouterOptionsTests
         Assert.Equal(AuthorizationMappingStrategy.Hybrid, options.AuthorizationMapping);
         Assert.Equal(MissingAuthorizationBehavior.WarnAndAllow, options.OnMissingAuthorization);
         Assert.Equal(TimeSpan.FromSeconds(30), options.DefaultTimeout);
-        Assert.Equal(TimeSpan.FromSeconds(10), options.HeartbeatInterval);
+        Assert.Equal(TimeSpan.FromSeconds(45), options.HeartbeatInterval);
     }
 
     [Fact]

src/Router/__Tests/StellaOps.Router.Transport.InMemory.Tests/InMemoryTransportOptionsTests.cs

@@ -43,24 +43,24 @@ public sealed class InMemoryTransportOptionsTests
 
     [Trait("Category", TestCategories.Unit)]
         [Fact]
-    public void Constructor_HeartbeatInterval_Is10Seconds()
+    public void Constructor_HeartbeatInterval_Is45Seconds()
     {
         // Arrange & Act
         var options = new InMemoryTransportOptions();
 
         // Assert
-        options.HeartbeatInterval.Should().Be(TimeSpan.FromSeconds(10));
+        options.HeartbeatInterval.Should().Be(TimeSpan.FromSeconds(45));
     }
 
     [Trait("Category", TestCategories.Unit)]
         [Fact]
-    public void Constructor_HeartbeatTimeout_Is30Seconds()
+    public void Constructor_HeartbeatTimeout_Is135Seconds()
     {
         // Arrange & Act
         var options = new InMemoryTransportOptions();
 
         // Assert
-        options.HeartbeatTimeout.Should().Be(TimeSpan.FromSeconds(30));
+        options.HeartbeatTimeout.Should().Be(TimeSpan.FromSeconds(135));
     }
 
     #endregion