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

src/components/portal/portal-shell.tsx

@@ -105,16 +105,18 @@ export function PortalShell({ children }: PortalShellProps) {
                 ) : null}
               </div>
             </div>
-            <Button
-              size="sm"
-              variant="outline"
-              onClick={handleSignOut}
-              disabled={isSigningOut}
-              className="inline-flex items-center gap-2"
-            >
-              <LogOut className="size-4" />
-              Sair
-            </Button>
+            {!machineContext ? (
+              <Button
+                size="sm"
+                variant="outline"
+                onClick={handleSignOut}
+                disabled={isSigningOut}
+                className="inline-flex items-center gap-2"
+              >
+                <LogOut className="size-4" />
+                Sair
+              </Button>
+            ) : null}
           </div>
         </div>
       </header>