fix: add numpy, httpx, version pins to backend/requirements.txt

Author: DHANUSHGCODE

backend/requirements.txt

@@ -1,8 +1,21 @@
-fastapi
-uvicorn
-pandas
-scikit-learn
-joblib
-python-multipart
-requests
-sqlalchemy
+# Backend API dependencies
+fastapi>=0.104.0
+uvicorn[standard]>=0.24.0
+
+# Data processing & ML
+numpy>=1.24.0
+pandas>=2.0.0
+scikit-learn>=1.3.0
+joblib>=1.3.0
+
+# Database
+sqlalchemy>=2.0.0
+
+# File uploads & HTTP
+python-multipart>=0.0.6
+requests>=2.31.0
+httpx>=0.25.0
+
+# Testing
+pytest>=7.4.0
+pytest-cov>=4.1.0