fix(mpc-service): increase Kafka consumer session timeout

- Increase sessionTimeout from 30s to 5 minutes
- Increase heartbeatInterval from 3s to 10s
- Add rebalanceTimeout of 5 minutes
- This prevents consumer from being kicked out during long MPC keygen operations

🤖 Generated with [Claude Code](https://claude.com/claude-code)

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

backend/services/mpc-service/src/infrastructure/messaging/kafka/event-consumer.service.ts

@@ -66,8 +66,10 @@ export class EventConsumerService implements OnModuleInit, OnModuleDestroy {
 
     this.consumer = this.kafka.consumer({
       groupId,
-      sessionTimeout: 30000,
-      heartbeatInterval: 3000,
+      sessionTimeout: 300000, // 5 minutes - MPC keygen can take a while
+      heartbeatInterval: 10000, // 10 seconds
+      maxWaitTimeInMs: 5000,
+      rebalanceTimeout: 300000, // 5 minutes
     });
 
     try {