feat: add periodic health check to evict dead instances

Add quarkus-scheduler dependency and schedule health check every 10 seconds.
Dead instances (marked with state="DEAD") now automatically evicted instead of
accumulating indefinitely.

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

modules/coordinator/build.gradle.kts

@@ -78,6 +78,7 @@ dependencies {
     implementation("com.fasterxml.jackson.module:jackson-module-scala_3:${versions["JACKSON_SCALA"]!!}")
     implementation("io.quarkus:quarkus-redis-client")
     implementation("io.quarkus:quarkus-kubernetes-client")
+    implementation("io.quarkus:quarkus-scheduler")
 
     testImplementation(platform("org.junit:junit-bom:${versions["JUNIT_BOM"]!!}"))
     testImplementation("org.junit.jupiter:junit-jupiter")

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

@@ -5,6 +5,7 @@ import jakarta.enterprise.context.ApplicationScoped
 import jakarta.enterprise.event.Observes
 import jakarta.enterprise.inject.Instance
 import jakarta.inject.Inject
+import io.quarkus.scheduler.Scheduled
 import de.nowchess.coordinator.config.CoordinatorConfig
 import io.fabric8.kubernetes.client.KubernetesClient
 import io.fabric8.kubernetes.api.model.Pod
@@ -73,7 +74,12 @@ class HealthMonitor:
       Thread.ofVirtual().start(() => validateStartupInstances(timeoutMs))
     startPodWatch()
 
-  def checkInstanceHealth: Unit =
+  @Scheduled(every = "10s")
+  def periodicHealthCheck(): Unit =
+    try checkInstanceHealth()
+    catch case ex: Exception => log.warnf(ex, "Health check failed")
+
+  def checkInstanceHealth(): Unit =
     meterRegistry.counter("nowchess.coordinator.health.checks").increment()
     val evicted = instanceRegistry.evictStaleInstances(config.instanceDeadTimeout)
     if evicted.nonEmpty then