Fix: SSO Login Page (#5220)

Users logging in via OAuth2 were redirected to Spring's default login
form instead of the React frontend login page. This happened because the
OAuth2 configuration used `.loginPage("/oauth2")` which pointed to the
old Thymeleaf template.

### Testing (if applicable)

- [x] I have tested my changes locally. Refer to the [Testing
Guide](https://github.com/Stirling-Tools/Stirling-PDF/blob/main/devGuide/DeveloperGuide.md#6-testing)
for more details.

app/core/src/main/java/stirling/software/SPDF/config/OpenApiConfig.java

@@ -66,7 +66,8 @@ public class OpenApiConfig {
         if (swaggerServerUrl != null && !swaggerServerUrl.trim().isEmpty()) {
             server = new Server().url(swaggerServerUrl).description("API Server");
         } else {
-            // Use relative path so Swagger uses the current browser origin to avoid CORS issues when accessing via different ports
+            // Use relative path so Swagger uses the current browser origin to avoid CORS issues
+            // when accessing via different ports
             server = new Server().url("/").description("Current Server");
         }
         openAPI.addServersItem(server);