fix(frontend): 进房后侧栏未读角标不再被 refresh 写回

应用会话列表时强制清零当前房间未读，并在已读成功事件后再清一次。

Co-authored-by: Cursor <cursoragent@cursor.com>

frontend/app/chat/ChatShell.tsx

@@ -112,14 +112,26 @@ export default function ChatShell({
   } | null>(null);
   const longPressTimer = useRef<ReturnType<typeof setTimeout> | null>(null);
 
+  /** 拉列表/SSR 回填时，当前打开的会话未读一律置 0（已读请求可能尚未落库） */
+  const applyRooms = useCallback(
+    (list: ChatRoomView[]) => {
+      const next = (list || []).map((r) =>
+        activeRoomId && r.id === activeRoomId ? { ...r, unread_count: 0 } : r
+      );
+      setRooms(sortRooms(next));
+    },
+    [activeRoomId]
+  );
+
   useEffect(() => {
-    setRooms(sortRooms(initialRooms));
-  }, [initialRooms]);
+    applyRooms(initialRooms);
+  }, [initialRooms, applyRooms]);
 
   const roomsInFlight = useRef(false);
   const lastRoomsFetchAt = useRef(0);
 
-  const refreshRooms = useCallback(async (opts?: { force?: boolean }) => {
+  const refreshRooms = useCallback(
+    async (opts?: { force?: boolean }) => {
       const now = Date.now();
       if (!opts?.force) {
         if (roomsInFlight.current) return;
@@ -130,13 +142,15 @@ export default function ChatShell({
       lastRoomsFetchAt.current = now;
       try {
         const res = await apiListChatRooms(1, 50, "", "joined");
-      setRooms(sortRooms(res.rooms || []));
+        applyRooms(res.rooms || []);
       } catch {
         // 静默
       } finally {
         roomsInFlight.current = false;
       }
-  }, []);
+    },
+    [applyRooms]
+  );
 
   // 进入消息壳 / 切会话：HTTP 拉最新排序（避开预取缓存）
   useEffect(() => {
@@ -194,12 +208,17 @@ export default function ChatShell({
     return off;
   }, [refreshRooms]);
 
-  // 进入会话后清零该会话未读
+  // 进房即清角标；MarkRead 成功后再清一次（防 refresh 抢在已读落库前写回旧未读）
   useEffect(() => {
     if (!activeRoomId) return;
+    const clearActiveUnread = () => {
       setRooms((prev) =>
         prev.map((r) => (r.id === activeRoomId ? { ...r, unread_count: 0 } : r))
       );
+    };
+    clearActiveUnread();
+    window.addEventListener("j13-chat-unread-sync", clearActiveUnread);
+    return () => window.removeEventListener("j13-chat-unread-sync", clearActiveUnread);
   }, [activeRoomId]);
 
   // 搜索：会话本地过滤 + 用户远程搜索