[Bug] `enable_audit_log` configuration not taking effect - always shows false despite correct setup

### Search before asking

- [x] I searched in the [issues](https://github.com/apache/iotdb/issues) and found nothing similar.

### Version

- **Versions Tested**: 2.0.5, 2.0.4, 2.0.3, 1.3.4-1 (standalone mode)
- **Deployment**: Docker (apache/iotdb:*-standalone images)

### Describe the bug and provide the minimal reproduce step

1. Set configuration via environment variable or in `iotdb-system.properties`:
```yaml
environment:
- enable_audit_log=true
```

2. Check runtime configuration:
```bash
docker logs iotdb-service 2>&1 | grep -i "enableAuditLog"
```

### What did you expect to see?

**Expected:**
```
enableAuditLog=true;
```

### What did you see instead?

**Actual:**
```
enableAuditLog=false;
```

### Anything else?

1. Configuration file contains `enable_audit_log=true` correctly
2. Startup log shows: `append enable_audit_log=true /iotdb/conf/iotdb-system.properties`
3. But runtime always shows: `enableAuditLog=false;`
4. Audit log file `/iotdb/logs/log_datanode_audit.log` is created but remains empty

### Are you willing to submit a PR?

- [ ] I'm willing to submit a PR!

まず、スタンドアロンの Docker イメージ apache/iotdb で設定を再現し、/iotdb/conf/iotdb-system.properties、起動ログ、および enableAuditLog のランタイム出力を調べます。enable_audit_log がランタイム設定に読み込まれる仕組みを追跡し、その後 enableAuditLog が true になり、/iotdb/logs/log_datanode_audit.log に監査イベントが記録されることを確認します。

索引モデルが issue の本文から書いたものです。