[web] Hive 4.0.0-dev.2 - issues initializing

Hello - I know that 4.0.0 is still a pre-release. I encountered a few issues while getting started on web.

The first issue is it seems to be expecting a directory:
```
Invalid argument(s) (directory): No directory specified and no defaultDirectory provided.
```

If we set the `Hive.defaultDirectory = ''` it seems to move ahead, but this time we get a different error:

```
On web you have to call Isar.initialize() manually before using Isar.
```

Calling `Isar.initialize()` throws the following error:
```
IsarError: Operation not supported. You might need to use a different flavor of Isar.
```

Does this mean we need to install `Isar` as well? Is there documentation that can help setup Hive for web?

Start by reproducing the web setup with Hive.defaultDirectory set to an empty string, then call Isar.initialize() and compare each failure with the current web setup documentation. Determine whether the expected result is a supported initialization path or clearer documentation; done means the documented web setup works without these errors.

Written by the indexing model from the issue text.