chat fixes

Focus: textarea gets refocused via inputRef after the AI response (or error) lands
Persistence: chat history saved to localStorage keyed by trip ID, loaded on mount — survives refreshes

drb-frontend/app/trips/[id]/page.tsx

@@ -497,6 +497,8 @@ interface SuggestionCard {
   added?: boolean;
 }
 
+const CHAT_STORAGE_KEY = (tripId: string) => `drb-trip-chat-${tripId}`;
+
 function AssistantPanel({
   trip,
   onAddEvent,
@@ -504,15 +506,26 @@ function AssistantPanel({
   trip: TripRecord & { events: TripEvent[] };
   onAddEvent: (event: TripEvent) => void;
 }) {
-  const [messages,  setMessages]  = useState<ChatMessage[]>([]);
+  const storageKey = CHAT_STORAGE_KEY(trip.trip_id);
+  const [messages,  setMessages]  = useState<ChatMessage[]>(() => {
+    try {
+      const saved = localStorage.getItem(storageKey);
+      return saved ? JSON.parse(saved) : [];
+    } catch { return []; }
+  });
   const [input,     setInput]     = useState("");
   const [loading,   setLoading]   = useState(false);
-  const bottomRef = useRef<HTMLDivElement>(null);
+  const bottomRef  = useRef<HTMLDivElement>(null);
+  const inputRef   = useRef<HTMLTextAreaElement>(null);
 
   useEffect(() => {
     bottomRef.current?.scrollIntoView({ behavior: "smooth" });
   }, [messages]);
 
+  useEffect(() => {
+    try { localStorage.setItem(storageKey, JSON.stringify(messages)); } catch { /* quota */ }
+  }, [messages, storageKey]);
+
   async function send() {
     const text = input.trim();
     if (!text || loading) return;
@@ -540,6 +553,7 @@ function AssistantPanel({
       ]);
     } finally {
       setLoading(false);
+      inputRef.current?.focus();
     }
   }
 
@@ -703,6 +717,7 @@ function AssistantPanel({
       <div className="px-3 py-3 border-t border-gray-800 shrink-0">
         <div className="flex gap-2">
           <textarea
+            ref={inputRef}
             value={input}
             onChange={(e) => { setInput(e.target.value); e.target.style.height = "auto"; e.target.style.height = `${Math.min(e.target.scrollHeight, 120)}px`; }}
             onKeyDown={(e) => e.key === "Enter" && !e.shiftKey && (e.preventDefault(), send())}