fix: harden dashboard message state

frontend/src/App.tsx

@@ -29,7 +29,15 @@ export default function App() {
     const ws = connectDashboardSocket((event: DashboardEvent) => {
       switch (event.type) {
         case "message_created":
-          setMessages((prev) => [event.data, ...prev].slice(0, 200));
+          setMessages((prev) => {
+            const existing = prev.some((message) => message.id === event.data.id);
+            if (existing) {
+              return prev.map((message) =>
+                message.id === event.data.id ? event.data : message,
+              );
+            }
+            return [event.data, ...prev].slice(0, 200);
+          });
           break;
         case "message_analyzed":
           setMessages((prev) =>

frontend/src/api/client.ts

@@ -29,16 +29,7 @@ export interface PageResult<T> {
   nextCursor: string | null;
 }
 
-export interface DashboardMessage {
-  id: string;
-  channel_id: string;
-  user_id: string;
-  username: string;
-  avatar_url: string | null;
-  content: string;
-  created_at: number;
-  type: "text" | "image" | "voice";
-}
+export type DashboardMessage = MessageRecord;
 
 export interface Guild {
   id: string;

frontend/src/components/messages/MessageCard.tsx

@@ -60,6 +60,7 @@ export function MessageCard({ message, onReanalyze }: MessageCardProps) {
 
         <div className="message-card-actions">
           <button
+            type="button"
             className="btn-reanalyze"
             onClick={() => onReanalyze(message.id)}
             disabled={aiStatus === "pending"}