chore(portal): ocultar opção de sair para sessões do agente

src/components/portal/portal-shell.tsx

@@ -105,6 +105,7 @@ export function PortalShell({ children }: PortalShellProps) {
                 ) : null}
               </div>
             </div>
+            {!machineContext ? (
               <Button
                 size="sm"
                 variant="outline"
@@ -115,6 +116,7 @@ export function PortalShell({ children }: PortalShellProps) {
                 <LogOut className="size-4" />
                 Sair
               </Button>
+            ) : null}
           </div>
         </div>
       </header>