Bi-column layout error with visual separator

### Bug

Docling is unable to recognize a separator line. See below

### Steps to reproduce
Start docling-serve:

`docker run --rm -e DOCLING_SERVE_ENABLE_UI=true -p 5001:5001 quay.io/docling-project/docling-serve:v0.6.0
`

Then browse to the ui. Choose url convert and paste the following url:
[https://www.amundi.lu/professional/dl/doc/prospectus/LU1807499428/ENG/LUX](https://www.amundi.lu/professional/dl/doc/prospectus/LU1807499428/ENG/LUX)

Choose the following options:


Now go to page 5:


**Expected**:
docling takes into account the separator line in the middle of the page, so that the paragraph Management Process will continue on the second column.

```
Management Process
The Sub-Funds... for the Sub-Fund.
Therefore, for the purpose... Risk Management method Commitment

----
Planning your investment...
```

**Current**:
Docling process the first column, then the second column without taking into account the middle separator line.


```
Management Process
The Sub-Funds... for the Sub-Fund.
----
Planning your investment...

Therefore, for the purpose... Risk Management method Commitment
```

### Docling version

2.25.1

### Python version
3.12.9