feat: persist AI chat history to server-side JSON file

Chat history was stored only in sessionStorage, causing member ID and DOB
to be lost when the session expired or corrupted — requiring logout/login.
Now history is saved to a per-user JSON file on the backend and loaded on
mount, so the LLM always has full conversation context.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

apps/Frontend/src/components/layout/chatbot.tsx

@@ -128,6 +128,28 @@ function loadSavedMessages(): Message[] {
   return [makeMsg("bot", "Hi! What can I help you with today?")];
 }
 
+const WELCOME = [makeMsg("bot", "Hi! What can I help you with today?")];
+
+let saveTimer: ReturnType<typeof setTimeout> | null = null;
+function saveChatHistoryToServer(msgs: Message[]) {
+  if (saveTimer) clearTimeout(saveTimer);
+  saveTimer = setTimeout(() => {
+    const saveable = msgs.filter((m) => !m.isLoading);
+    fetch("/api/ai/chat-history", {
+      method: "PUT",
+      headers: { "Content-Type": "application/json", Authorization: `Bearer ${localStorage.getItem("token") ?? ""}` },
+      body: JSON.stringify({ messages: saveable }),
+    }).catch(() => {});
+  }, 500);
+}
+
+function clearChatHistoryOnServer() {
+  fetch("/api/ai/chat-history", {
+    method: "DELETE",
+    headers: { Authorization: `Bearer ${localStorage.getItem("token") ?? ""}` },
+  }).catch(() => {});
+}
+
 export function ChatbotButton() {
   const [open, setOpen] = useState(false);
   const [step, setStep] = useState<Step>("menu");
@@ -173,15 +195,36 @@ export function ChatbotButton() {
   const freeTextRef = useRef<HTMLTextAreaElement>(null);
   const fileInputRef = useRef<HTMLInputElement>(null);
 
+  // Load chat history from server on first mount (server is source of truth)
+  const serverLoaded = useRef(false);
+  useEffect(() => {
+    if (serverLoaded.current) return;
+    serverLoaded.current = true;
+    const token = localStorage.getItem("token");
+    if (!token) return;
+    fetch("/api/ai/chat-history", {
+      headers: { Authorization: `Bearer ${token}` },
+    })
+      .then((r) => r.json())
+      .then((data) => {
+        if (Array.isArray(data.messages) && data.messages.length > 0) {
+          setMessages(data.messages);
+          try { sessionStorage.setItem(CHAT_STORAGE_KEY, JSON.stringify(data.messages)); } catch {}
+        }
+      })
+      .catch(() => {});
+  }, []);
+
   useEffect(() => {
     messagesEndRef.current?.scrollIntoView({ behavior: "smooth" });
   }, [messages, step]);
 
-  // Persist messages across navigation (cleared on logout)
+  // Persist messages to sessionStorage AND server
   useEffect(() => {
     try {
       const saveable = messages.filter((m) => !m.isLoading);
       sessionStorage.setItem(CHAT_STORAGE_KEY, JSON.stringify(saveable));
+      saveChatHistoryToServer(messages);
     } catch {}
   }, [messages]);
 
@@ -230,6 +273,7 @@ export function ChatbotButton() {
     try {
       sessionStorage.setItem(CHAT_STORAGE_KEY, JSON.stringify(fresh));
     } catch {}
+    clearChatHistoryOnServer();
     setMessages(fresh);
   };