Move the Auth with GitLab to the Group Level

We need the UNLOCODE Gitlab to be able to 'vouch for' a user requesting a DMR on unlocode.unece.org to do this we need to register the application to enable OAuth.

I have done this on my user settings for the POC but it will be better at the group level in Gitlab which then survives any personnel changes and can be used by other sites developed in UNECE on GitLab

1. Sign in to opensource.unicc.org as someone who can register applications.
2. At /-/user_settings/applications (or admin equivalent), create a new app: - Name: UN/LOCODE contributor portal - Redirect URIs (one per line):
   • http://localhost:3000/contribute/auth
   • https://vocab-locode-40898c.opensource.unicc.org/contribute/auth
   • (production custom domain + /contribute/auth when you have one) - Confidential: unchecked (it's a public client; PKCE replaces the secret) - Scopes: read_api
3. Copy the Application ID and paste it into website/static/data/oauth-config.json as clientId.

Until step 3 is done, the banner shows "OAuth is not configured yet" with a link to /contribute/oauth-setup (full walkthrough).