Only includes data that is provided in the first row

In a stream looking like this:

```
{"a": 1}
{"a":1,"b":2}
```

the `b` would not be shown in the table. However to solve this the whole data would need to be loaded into memory, since the head has to be provided first.

I think the only solution would be so solve it on the client side.

Start by reproducing the example stream and inspect how the NDJSON rows become an HTML table, especially how columns are determined from the first row. Decide how client-side handling should expose fields introduced later without loading the entire stream, then verify that the `b` column appears for the second example row.

Written by the indexing model from the issue text.