Add initial project structure with .gitignore, pyproject.toml, and main application files

src/app.py

@@ -0,0 +1,39 @@
+import streamlit as st
+from openai_client import OpenAIClient
+
+def init_session_state():
+    if "messages" not in st.session_state:
+        st.session_state.messages = []
+
+def display_chat_messages():
+    for message in st.session_state.messages:
+        with st.chat_message(message["role"]):
+            st.markdown(message["content"])
+
+def handle_user_input():
+    if prompt := st.chat_input("Type your message..."):
+        st.session_state.messages.append({"role": "user", "content": prompt})
+        with st.chat_message("user"):
+            st.markdown(prompt)
+        
+        with st.chat_message("assistant"):
+            response_placeholder = st.empty()
+            full_response = ""
+            
+            client = OpenAIClient()
+            for chunk in client.get_chat_response(st.session_state.messages):
+                if chunk.choices[0].delta.content:
+                    full_response += chunk.choices[0].delta.content
+                    response_placeholder.markdown(full_response + "▌")
+            
+            response_placeholder.markdown(full_response)
+            st.session_state.messages.append({"role": "assistant", "content": full_response})
+
+def main():
+    st.title("Streamlit Chat App")
+    init_session_state()
+    display_chat_messages()
+    handle_user_input()
+
+if __name__ == "__main__":
+    main()