build(deps): bump pymdown-extensions from 10.11.2 to 10.14.2 in /backend

Bumps [pymdown-extensions](https://github.com/facelessuser/pymdown-extensions) from 10.11.2 to 10.14.2.
- [Release notes](https://github.com/facelessuser/pymdown-extensions/releases)
- [Commits](https://github.com/facelessuser/pymdown-extensions/compare/10.11.2...10.14.2)

---
updated-dependencies:
- dependency-name: pymdown-extensions
  dependency-type: direct:production
  update-type: version-update:semver-minor
...

Signed-off-by: dependabot[bot] <support@github.com>

backend/requirements.txt

@@ -57,7 +57,7 @@ einops==0.8.0
 ftfy==6.2.3
 pypdf==4.3.1
 fpdf2==2.8.2
-pymdown-extensions==10.11.2
+pymdown-extensions==10.14.2
 docx2txt==0.8
 python-pptx==1.0.0
 unstructured==0.15.9