fix: use ChannelStore for activeChannelId subscription

activeChannelId lives on ChannelStore, not ServerStore.

web/src/components/Layout.tsx

@@ -3,6 +3,7 @@ import { Link, Outlet, useLocation, useNavigate } from 'react-router-dom';
 import { useAuthStore, type UserStatus } from '../stores/auth.ts';
 import { useWebSocketStore } from '../stores/ws.ts';
 import { useServerStore } from '../stores/server.ts';
+import { useChannelStore } from '../stores/channel.ts';
 import { useLayoutStore } from '../stores/layout.ts';
 import { ServerBar } from './ServerBar.tsx';
 import { ChannelList } from './ChannelList.tsx';
@@ -42,7 +43,7 @@ export function Layout() {
   const setMobileView = useLayoutStore((s) => s.setMobileView);
   const [showServerSettings, setShowServerSettings] = useState(false);
   const activeServerId = useServerStore((s) => s.activeServerId);
-  const activeChannelId = useServerStore((s) => s.activeChannelId);
+  const activeChannelId = useChannelStore((s) => s.activeChannelId);
   useEffect(() => {
     wsConnect();
     return () => { wsDisconnect(); };
@@ -54,7 +55,7 @@ export function Layout() {
   }, [isLoading, isAuthenticated, location.pathname, navigate]);
   // Navigate to chat when a channel/DM is selected on mobile
   useEffect(() => {
-    const unsub = useServerStore.subscribe((state, prev) => {
+    const unsub = useChannelStore.subscribe((state, prev) => {
       if (state.activeChannelId !== prev.activeChannelId && state.activeChannelId) {
         setMobileView('chat');
       }