Add fastapi for backend imports

Author: snigdhareddy482

requirements.txt

@@ -3,7 +3,12 @@ streamlit>=1.39.0
 pydantic>=2.9.0
 requests>=2.32.0
 
-# Document Processing (newer versions for Py 3.13)
+# Backend imports need these
+fastapi>=0.109.0
+uvicorn>=0.27.0
+python-multipart>=0.0.9
+
+# Document Processing
 python-docx>=1.1.0
 fpdf2>=2.7.0
 Pillow>=10.4.0