fix(slave_node): Stabilize Modbus RTU communication

The Modbus server was previously unstable, leading to intermittent CRC errors when polled by a master. This was caused by the main thread exiting after initialization, which created timing and race condition issues for the interrupt-driven Modbus stack.

This fix ensures the main thread continues to run in a low-power sleep loop (). This provides a stable context for the Modbus server, resolving the CRC errors and ensuring reliable communication.

software/apps/slave_node/src/main.c

@@ -111,5 +111,10 @@ int main(void)
 		LOG_ERR("Modbus RTU server initialization failed");
 	}
 	LOG_INF("APP started");
+	
+	while (1) {
+		k_sleep(K_MSEC(1000));
+	}
+
 	return 0;
-}
+}