[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/connection.go

@@ -42,11 +42,6 @@ type WaitSSOParams struct {
 type UpParams struct {
 	ProfileName string `json:"profileName"`
 	Username    string `json:"username"`
-	// Async instructs the daemon to start the connection and return
-	// immediately. Status updates flow via the SubscribeStatus stream.
-	// When false (the default) the RPC blocks until connected, which is
-	// the CLI behaviour.
-	Async bool `json:"async"`
 }
 
 // LogoutParams selects the profile the daemon should log out.
@@ -152,7 +147,8 @@ func (s *Connection) Up(ctx context.Context, p UpParams) error {
 	if err != nil {
 		return err
 	}
-	req := &proto.UpRequest{Async: p.Async}
+	// The UI always uses async mode: status updates flow via SubscribeStatus.
+	req := &proto.UpRequest{Async: true}
 	if p.ProfileName != "" {
 		req.ProfileName = ptrStr(p.ProfileName)
 	}

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)
 		}