fix(mining-admin-service): ignore Debezium heartbeat messages

- Add isHeartbeatMessage to detect heartbeat messages (only have ts_ms field)
- Skip processing for heartbeat messages to avoid unnecessary warnings

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

backend/services/mining-admin-service/src/infrastructure/kafka/cdc-consumer.service.ts

@@ -174,6 +174,11 @@ export class CdcConsumerService implements OnModuleInit, OnModuleDestroy {
       const eventData = JSON.parse(message.value.toString());
       const sequenceNum = BigInt(message.offset);
 
+      // 忽略 Debezium 心跳消息 (只有 ts_ms 字段)
+      if (this.isHeartbeatMessage(eventData)) {
+        return;
+      }
+
       // 判断事件类型：Debezium CDC 或 服务 Outbox 事件
       if (this.isDebeziumEvent(eventData)) {
         // Debezium outbox 事件：从 payload.after 提取服务事件
@@ -198,6 +203,15 @@ export class CdcConsumerService implements OnModuleInit, OnModuleDestroy {
     }
   }
 
+  /**
+   * 判断是否为 Debezium 心跳消息
+   * 心跳消息格式: { ts_ms: number }
+   */
+  private isHeartbeatMessage(data: any): boolean {
+    const keys = Object.keys(data);
+    return keys.length === 1 && keys[0] === 'ts_ms';
+  }
+
   private isDebeziumEvent(data: any): boolean {
     return data.payload && data.payload.source && data.payload.op;
   }