CVE-2026-42223: Nginx-UI Settings API Exposes Protected Secrets

The GetSettings API handler (api/settings/settings.go:24-65) serializes all settings structs to JSON and returns them to authenticated users. Many sensitive fields are tagged with protected:"true" - however, this tag is only enforced during writes (via ProtectedFill in SaveSettings) and is completely ignored during reads. This exposes 40+ protected fields including JwtSecret (enabling auth token forgery), NodeSecret (enabling cluster node impersonation), OIDC ClientSecret (enabling OAuth account takeover), and the IP whitelist configuration.