Add UI test for OIDCPolicy form view

## Details
OIDCPolicy form has: policy name, target gateway, clientID, issuerURL.

## Checklist
- [ ] Policy name required field validation
- [ ] Target gateway selector validation
- [ ] Client ID field validation
- [ ] Issuer URL field validation
- [ ] Form/YAML toggle preserves data
- [ ] Form submission creates resource
- [ ] Edit mode loads existing resource
- [ ] Cancel redirects to list page