feat: route desktop matrix: deep links into the client

Adds useDeepLinkNavigate (mounted in ClientNonUIFeatures): listens for the
'lotus-deeplink' DOM CustomEvent that the Tauri shell dispatches when a
matrix:/matrix.to link opens the app, converts matrix: URIs to matrix.to, and
navigates via the same path as useMentionClickHandler (reusing matrix-to.ts
parsers + useRoomNavigate). No-op outside Tauri.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

src/app/pages/client/ClientNonUIFeatures.tsx

@@ -34,6 +34,7 @@ import { useSelectedRoom } from '../../hooks/router/useSelectedRoom';
 import { useInboxNotificationsSelected } from '../../hooks/router/useInbox';
 import { useMediaAuthentication } from '../../hooks/useMediaAuthentication';
 import { usePresenceUpdater } from '../../hooks/usePresenceUpdater';
+import { useDeepLinkNavigate } from '../../hooks/useDeepLinkNavigate';
 import { toastQueueAtom } from '../../state/toast';
 
 function isInQuietHours(start: string, end: string): boolean {
@@ -376,6 +377,11 @@ type ClientNonUIFeaturesProps = {
   children: ReactNode;
 };
 
+function DeepLinkNavigator() {
+  useDeepLinkNavigate();
+  return null;
+}
+
 export function ClientNonUIFeatures({ children }: ClientNonUIFeaturesProps) {
   return (
     <>
@@ -385,6 +391,7 @@ export function ClientNonUIFeatures({ children }: ClientNonUIFeaturesProps) {
       <PresenceUpdater />
       <InviteNotifications />
       <MessageNotifications />
+      <DeepLinkNavigator />
       {children}
     </>
   );