feat(P5C.T2): per-conv 'mentions only' toggle + notification gate

apps/desktop/src/pages/ChatsPage.tsx

@@ -425,6 +425,7 @@ function ConversationRow({
         conversationId={item.id}
         archived={item.archived}
         mutedUntil={item.mutedUntil}
+        mentionsOnly={item.mentionsOnly}
       />
     </NavLink>
   );