unhelpful error message when aggregate function is used in where clause

dolt
```
stocks/master> select max(date) as latest_date from ohlcv where max(date) < date_sub(curdate(), interval 7 day);
Error 1105 (HY000): unable to find field with index 8 in row of 1 columns
```

mysql
```
mysql> select max(date) as latest_date from ohlcv where max(date) < date_sub(curdate, interval 7 day);
ERROR 1111 (HY000): Invalid use of group function
```

Reproduce the Dolt query and compare its error with the MySQL result shown in the issue. Trace the SQL aggregation and WHERE-clause validation path responsible for the invalid field-index error. Done means the query returns a clear, appropriate invalid-use-of-group-function error instead of the internal field-index message.

Written by the indexing model from the issue text.