[server] Use per-table remote data directory when storing lake table offset files

### Search before asking

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

### Description

**Current Situation:**

`LakeTableHelper` stores the lake table snapshot offset file to a remote path derived from the global `remote.data.dir` configuration, which is injected at construction time:

```java
public LakeTableHelper(ZooKeeperClient zkClient, String remoteDataDir) {
this.zkClient = zkClient;
this.remoteDataDir = remoteDataDir;
}
```

`storeLakeTableOffsetsFile()` then builds the remote path using this fixed `remoteDataDir`:

```java
public FsPath storeLakeTableOffsetsFile(TablePath tablePath, TableBucketOffsets offsets)
```

With the introduction of multiple remote data directories (`remote.data.dirs`), each table is assigned its own `remoteDataDir` at creation time and persisted in `TableRegistration`. We should also store the lake snapshot offset file to the table's specific remote data dir.

### Willingness to contribute

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

Start by reading LakeTableHelper, especially its constructor and storeLakeTableOffsetsFile(), then trace how the table-specific remoteDataDir is persisted in TableRegistration. Confirm the existing offset-file path behavior and update the implementation so it uses the table's assigned directory; done means lake snapshot offset files are stored under that per-table location.

Written by the indexing model from the issue text.