feat: Add requirements.txt for project dependencies

Author: rahul-aot

backend/requirements.txt

@@ -1,6 +1,13 @@
-fastapi==0.115.6
-uvicorn[standard]==0.34.0
-pydantic==2.10.5
-pydantic-settings==2.7.1
-google-genai==1.11.1
-python-dotenv==1.0.1
+
+fastapi>=0.109.0
+uvicorn>=0.27.0
+
+pydantic>=2.6.0
+pydantic-settings>=2.1.0
+python-dotenv>=1.0.1
+
+python-multipart>=0.0.7
+httpx>=0.26.0
+
+faiss-cpu>=1.7.4
+google-genai>=1.0.0