fix(vikon): use form-encoded POST + correct domain for OAuth token exchange

- HttpTask::post() now sends application/x-www-form-urlencoded (not JSON)
- AuthenticateAction sends to db-nica.ru (not auth.db-nica.ru) matching original vikon_core
- Original code: remoteRequest($apiDomen . 'oauth2/authorize/token', ...)

app/Containers/VikonIntegration/Actions/Auth/AuthenticateAction.php

@@ -23,7 +23,7 @@ class AuthenticateAction
             'client_secret' => $this->clientSecret,
             'redirect_uri' => $redirectUri,
             'grant_type' => 'authorization_code',
-        ], 'auth');
+        ]);
 
         $body = $response->json();