feat(examples): add saas settings page fallback

Make the SaaS tutorial's settings route render a distinct full-page fallback while the enhanced handler still swaps the generated page panel and pushes history. This proves page-swap shape without relying only on the enhanced interaction path.

req: examples/001

req: page_swap/002

examples/saas/src/main.rs

@@ -6,7 +6,7 @@ use axum::Router;
 use futures_util::stream;
 use hemx::IntoEffect;
 use hemx_axum::{runtime_js, sse, EffectResponse, InteractionRequest};
-use hemx_saas_example::{home_page, live_status, registry, ui, AppContext};
+use hemx_saas_example::{home_page, live_status, registry, settings_page, ui, AppContext};
 use std::collections::BTreeMap;
 use std::convert::Infallible;
 
@@ -37,7 +37,7 @@ async fn home(State(ctx): State<AppContext>) -> impl IntoResponse {
 }
 
 async fn settings(State(ctx): State<AppContext>) -> impl IntoResponse {
-    axum::response::Html(home_page(&ctx).into_string())
+    axum::response::Html(settings_page(&ctx).into_string())
 }
 
 async fn interact(