fix: scale up immediately when instance is lost

When an instance is evicted or fails health check, immediately trigger scale-up
to replace the lost capacity. Don't wait for the next scheduled scale check.

HealthMonitor now calls autoScaler.scaleUp() when:
1. Stale instances are evicted
2. Instance fails health check and is marked dead

Ensures quick recovery from instance loss.

Co-Authored-By: Claude Haiku 4.5 <noreply@anthropic.com>

modules/coordinator/src/main/scala/de/nowchess/coordinator/service/HealthMonitor.scala

@@ -45,6 +45,9 @@ class HealthMonitor:
   @Inject
   private var failoverService: FailoverService = uninitialized
 
+  @Inject
+  private var autoScaler: AutoScaler = uninitialized
+
   private val log         = Logger.getLogger(classOf[HealthMonitor])
   private var redisPrefix = "nowchess"
   // scalafix:on DisableSyntax.var
@@ -85,14 +88,18 @@ class HealthMonitor:
     if evicted.nonEmpty then
       log.warnf("Evicted %d stale instances: %s", evicted.size, evicted.mkString(", "))
       evicted.foreach(deleteK8sPod)
-    val instances = instanceRegistry.getAllInstances
+      autoScaler.scaleUp()
+    val instances      = instanceRegistry.getAllInstances
+    var instanceFailed = false
     instances.foreach { inst =>
       val isHealthy = checkHealth(inst.instanceId)
       if !isHealthy && inst.state == "HEALTHY" then
         log.warnf("Instance %s marked unhealthy", inst.instanceId)
         instanceRegistry.markInstanceDead(inst.instanceId)
         deleteK8sPod(inst.instanceId)
+        instanceFailed = true
     }
+    if instanceFailed then autoScaler.scaleUp()
 
   private def checkHealth(instanceId: String): Boolean =
     val redisHealthy = checkRedisHeartbeat(instanceId)