feat(web)!: sign in before joining a space and drop the stranger option

Opening a space link while signed out shows the sign-in page first and keeps
the link in memory. The channel settings no longer offer the stranger switch,
and the client supports API contract major 8.

web/src/app/App.tsx

@@ -68,6 +68,8 @@ export function App() {
   else if (route.name === 'share' && waitingOnSavedShare) screen = null;
   else if (route.name === 'share') screen = <ShareScreen id={route.id} />;
   else if (route.name === 'channel' && waitingOnSavedChannel) screen = null;
+  // 空间只接受登录账号:未登录先登录,链接留在内存里,登录后继续加入
+  else if (route.name === 'channel' && !username) screen = <AccountScreen />;
   else if (saved) screen = <ChannelScreen id={route.id} />;
   else if (pendingLink?.id === route.id) {
     screen = (