[client/ui] Always use async Up in the UI service layer

The UI never needs to block on Up — status updates flow via the
SubscribeStatus stream. Hardcode Async:true in Connection.Up and remove
the Async field from UpParams so frontend callers are unaffected.

client/ui/services/profileswitcher.go

@@ -72,7 +72,6 @@ func (s *ProfileSwitcher) SwitchActive(ctx context.Context, p ProfileRef) error
 		if err := s.connection.Up(ctx, UpParams{
 			ProfileName: p.ProfileName,
 			Username:    p.Username,
-			Async:       true,
 		}); err != nil {
 			return fmt.Errorf("reconnect %q: %w", p.ProfileName, err)
 		}