ORCID: Added a guard before rendering the OAuth buttons

[pascal-meunier]

ticket https://nanohub.org/support/ticket/505173

Two changes made:

config/config.xml — Changed orcid_service default from "public" to "members". The XML default was "public" but every PHP code path uses 'members' as its
fallback, so if an admin ever saved the config page without explicitly choosing a service it would store "public" — and there's no orcid_public_client_id
field, making $clientID permanently empty.

models/fields/orcid.php — Added an $oauthConfigured guard before rendering the OAuth buttons:
$oauthConfigured = ($srv !== 'public' && !empty($clientID) && !empty($redirectURI));
The "Create or Connect" and "Grant Permission" buttons now only appear when:

• The service is not 'public' (which is documented as search-only)
• orcid_members_client_id (or sandbox) is actually filled in
• The redirect URI is configured

This prevents users from clicking a broken link that ORCID rejects. Until the admin configures orcid_members_client_id and orcid_members_redirect_uri in
Administrator → Components → Members → Options, the buttons will simply not appear.

[pascal-meunier]

config/config.xml is not included in this pull request because:
The following paths are ignored by one of your .gitignore files:
core/components/com_members/config
hint: Use -f if you really want to add them.
hint: Disable this message with "git config advice.addIgnoredFile false"