Simpler stateless chat interface that focuses on document-based assistance

- Replace conversation-based chat system with direct assistant API calls
- Remove ConversationList component and related conversation state management
- Switch from continueConversation to sendAssistantMessage API endpoint
- Track current messages and response IDs instead of full conversations
- Remove conversation creation, deletion, and title updating functionality
- Simplify UI by removing conversation list toggle and management buttons
- Update welcome message to focus on document-based Q&A instead of bipolar treatment
- Maintain backward compatibility by keeping Conversation interface export
- Remove DOM content extraction and page content tracking
- Streamline message handling with direct assistant responses

Author: sahilds1

frontend/src/api/apiClient.ts

@@ -267,6 +267,20 @@ const updateConversationTitle = async (
   }
 };
 
+// Assistant API functions
+const sendAssistantMessage = async (message: string, previousResponseId?: string) => {
+  try {
+    const response = await api.post(`/v1/api/assistant`, {
+      message,
+      previous_response_id: previousResponseId,
+    });
+    return response.data;
+  } catch (error) {
+    console.error("Error(s) during sendAssistantMessage: ", error);
+    throw error;
+  }
+};
+
 export {
   handleSubmitFeedback,
   handleSendDrugSummary,
@@ -279,5 +293,6 @@ export {
   updateConversationTitle,
   handleSendDrugSummaryStream,
   handleSendDrugSummaryStreamLegacy,
-  fetchRiskDataWithSources
+  fetchRiskDataWithSources,
+  sendAssistantMessage
 };