Issue found on page 'Aggregate Functions': quantile_cont(x, pos) aggregate function takes value in the range [-1, 1] for pos, needs documentation

The docs for aggregate function quantile_cont(x, pos) read:

> The interpolated pos-quantile of x for 0 <= pos <= 1,

But when we enter an out of range value, the error message tells us the range for `pos `is `[-1, 1]`:

```
select quantile_cont(x, 2)
from range(0,100) as T(x)
```
output:
```
Binder Error: QUANTILE can only take parameters in the range [-1, 1]
```

When I try to use negative values within the range, it appears as if negative values are interpreted to "counting backwards", as if for for 0 < y <=1,

`quantile_cont(x, -y)`
is equivalent to
`quantile_cont(x, 1-y)`

For example:
```
SELECT quantile_cont(x, -0.1) as "q-0.1"
, quantile_cont(x, 1 - 0.1) as "q1-0.1"
, "q-0.1" = "q1-0.1" as "eq"
from range(0, 100) as T(x)
```
output:
```
┌───────────────────┬───────────────────┬─────────┐
│ q-0.1 │ q1-0.1 │ eq │
│ double │ double │ boolean │
├───────────────────┼───────────────────┼─────────┤
│ 89.10000000000001 │ 89.10000000000001 │ true │
└───────────────────┴───────────────────┴─────────┘
```

Page URL: [](https://duckdb.org/docs/sql/functions/aggregates#quantile_contx-pos)

Open the Aggregate Functions documentation at the linked page and inspect the quantile_cont(x, pos) section. Verify the documented range against the shown error and examples, then update the explanation to cover the observed negative-value behavior; done means the page accurately describes valid pos values and their interpretation.

Written by the indexing model from the issue text.