feat(search): focus and highlight found message in chat

- store focused message id per chat
- scroll to target message and highlight it after search selection
- clear focus automatically after short timeout

web/src/store/chatStore.ts

@@ -12,6 +12,7 @@ interface ChatState {
   typingByChat: Record<number, number[]>;
   replyToByChat: Record<number, Message | null>;
   unreadBoundaryByChat: Record<number, number>;
+  focusedMessageIdByChat: Record<number, number | null>;
   loadChats: (query?: string) => Promise<void>;
   setActiveChatId: (chatId: number | null) => void;
   loadMessages: (chatId: number) => Promise<void>;
@@ -44,6 +45,7 @@ interface ChatState {
   applyPresenceEvent: (chatId: number, userId: number, isOnline: boolean, lastSeenAt?: string) => void;
   setDraft: (chatId: number, text: string) => void;
   clearDraft: (chatId: number) => void;
+  setFocusedMessage: (chatId: number, messageId: number | null) => void;
 }
 
 export const useChatStore = create<ChatState>((set, get) => ({
@@ -56,6 +58,7 @@ export const useChatStore = create<ChatState>((set, get) => ({
   typingByChat: {},
   replyToByChat: {},
   unreadBoundaryByChat: {},
+  focusedMessageIdByChat: {},
   loadChats: async (query) => {
     const chats = await getChats(query);
     const currentActive = get().activeChatId;
@@ -342,5 +345,12 @@ export const useChatStore = create<ChatState>((set, get) => ({
       const next = { ...state.draftsByChat };
       delete next[chatId];
       return { draftsByChat: next };
-    })
+    }),
+  setFocusedMessage: (chatId, messageId) =>
+    set((state) => ({
+      focusedMessageIdByChat: {
+        ...state.focusedMessageIdByChat,
+        [chatId]: messageId
+      }
+    }))
 }));