Add shared models (Network, Host, Port, Application, ApplicationPort)
with serde derives for Leptos server function serialization.
Add server/validation.rs with valider_ip_dans_reseau() and 5 unit tests.
Gate SSR-only modules (config, validation) with #[cfg(feature = "ssr")].
Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>
