fix: .md processing issue

backend/requirements.txt

@@ -45,6 +45,7 @@ pypdf==4.3.1
 docx2txt==0.8
 python-pptx==1.0.0
 unstructured==0.15.7
+nltk==3.9.1
 Markdown==3.7
 pypandoc==1.13
 pandas==2.2.2

pyproject.toml

@@ -52,6 +52,7 @@ dependencies = [
     "docx2txt==0.8",
     "python-pptx==1.0.0",
     "unstructured==0.15.7",
+    "nltk==3.9.1",
     "Markdown==3.7",
     "pypandoc==1.13",
     "pandas==2.2.2",