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/__Libraries/StellaOps.Router.AspNet/StellaRouterOptionsBase.cs

@@ -39,9 +39,9 @@ public class StellaRouterOptionsBase
 
     /// <summary>
     /// Heartbeat interval in seconds for health reporting.
-    /// Default: 10 seconds.
+    /// Default: 45 seconds.
     /// </summary>
-    public int HeartbeatIntervalSeconds { get; set; } = 10;
+    public int HeartbeatIntervalSeconds { get; set; } = 45;
 
     /// <summary>
     /// Service trust mode for gateway-enforced authorization semantics.