fix(web-core): stabilize unread sync and realtime dedup behavior

- make prependMessage return insertion status for dedup-safe unread increments

- increment unread only on newly inserted incoming messages

- trigger chat list refresh on websocket reconnect to resync unread counters

web/src/store/chatStore.ts

@@ -12,7 +12,7 @@ interface ChatState {
   loadChats: (query?: string) => Promise<void>;
   setActiveChatId: (chatId: number | null) => void;
   loadMessages: (chatId: number) => Promise<void>;
-  prependMessage: (chatId: number, message: Message) => void;
+  prependMessage: (chatId: number, message: Message) => boolean;
   addOptimisticMessage: (params: {
     chatId: number;
     senderId: number;
@@ -70,11 +70,12 @@ export const useChatStore = create<ChatState>((set, get) => ({
   prependMessage: (chatId, message) => {
     const old = get().messagesByChat[chatId] ?? [];
     if (old.some((m) => m.id === message.id || (message.client_message_id && m.client_message_id === message.client_message_id))) {
-      return;
+      return false;
     }
     set((state) => ({
       messagesByChat: { ...state.messagesByChat, [chatId]: [...old, message] }
     }));
+    return true;
   },
   addOptimisticMessage: ({ chatId, senderId, type, text, clientMessageId }) => {
     const old = get().messagesByChat[chatId] ?? [];