Bad / corrupted paths for images under Microsoft Windows for `--image-export-mode referenced`

### Bug

Using command line tool docling to convert (say) PDF to; markdown, html, or html_split_page results in "bad" paths for Windows. Either '\' or URL encoded to `%5C`.

Looks like this is actually in docling-core https://github.com/docling-project/docling-core/blob/2a78701b3fcee511a3b0d5a6acdf82851d70cfe2/docling_core/types/doc/document.py#L5924 or the rendering https://github.com/docling-project/docling-core/blob/2a78701b3fcee511a3b0d5a6acdf82851d70cfe2/docling_core/transforms/serializer/html.py#L1200 - I'm not clear which

### Steps to reproduce

1. Needs a windows environment :-)
2. use sample doc and convert:

docling --no-ocr --to html --image-export-mode referenced tests\data\pdf\picture_classification.pdf

alternatively use Markdown or html.

Seeing

should be

`%5C` is `\`

trying markdown

docling --no-ocr --to md --image-export-mode referenced tests\data\pdf\picture_classification.pdf

seems fine but not ideal


so using windows path, I believe it is reasonable to use '/' in a Markdown file under Windows.

### Docling version

Docling version: 2.102.1
Docling Core version: 2.82.0
Docling IBM Models version: 3.13.3
Docling Parse version: 6.2.0
Python: cpython-312 (3.12.5)
Platform: Windows-11-10.0.22631-SP0

### Python version

Python 3.12.5