Gate RqueueJobMetricsAggregatorService on Redis backend

The aggregator depends on RqueueLockManager (Redis-only) and
RqueueQStatsDao (Redis-only); both were gated in the previous commit
but the aggregator @component itself wasn't, so its constructor
injection failed at startup with NoSuchBeanDefinitionException for
RqueueLockManager when rqueue.backend=nats. Adding
@conditional(RedisBackendCondition.class) on the aggregator keeps it
out of the context on the NATS path; metrics aggregation is a Redis
feature for v1 and the dashboard already hides the related panels.

Assisted-By: Claude Code

Author: sonus21

rqueue-core/src/main/java/com/github/sonus21/rqueue/web/service/RqueueJobMetricsAggregatorService.java

@@ -17,6 +17,7 @@
 package com.github.sonus21.rqueue.web.service;
 
 import com.github.sonus21.rqueue.common.RqueueLockManager;
+import com.github.sonus21.rqueue.config.RedisBackendCondition;
 import com.github.sonus21.rqueue.config.RqueueConfig;
 import com.github.sonus21.rqueue.config.RqueueWebConfig;
 import com.github.sonus21.rqueue.core.RqueueMessage;
@@ -51,11 +52,13 @@
 import org.springframework.beans.factory.annotation.Autowired;
 import org.springframework.context.ApplicationListener;
 import org.springframework.context.SmartLifecycle;
+import org.springframework.context.annotation.Conditional;
 import org.springframework.scheduling.concurrent.ThreadPoolTaskScheduler;
 import org.springframework.stereotype.Component;
 import org.springframework.util.CollectionUtils;
 
 @Component
+@Conditional(RedisBackendCondition.class)
 @Slf4j
 public class RqueueJobMetricsAggregatorService
     implements ApplicationListener<RqueueExecutionEvent>, DisposableBean, SmartLifecycle {