✨ (htmx): Añade soporte HTMX a tablas ordenables

- Nuevo `SortDir` en `pagetop::html` para representar direcciones de
  orden (asc/desc) y calcular la siguiente al pulsar una cabecera.
- `hx_table::sort_link()` construye el enlace de ordenación con los
  cuatro atributos `hx-*` fijos, reutilizable en cualquier tabla.
- `HtmxResponse` usa `RoutePath` en `location`/`push_url`/`replace_url`/
  `redirect` para preservar "lang"; `location_json()` se separa de
  `location()` para el caso de configuración JSON personalizada.
- Añade el módulo `prelude` y una batería de tests para hx, hx_table,
  request, response y extension.

extensions/pagetop-htmx/tests/extension.rs

@@ -0,0 +1,62 @@
+use pagetop::prelude::*;
+use pagetop_htmx::Htmx;
+
+struct TestApp;
+
+#[async_trait]
+impl Extension for TestApp {
+    fn dependencies(&self) -> Vec<ExtensionRef> {
+        vec![&Htmx]
+    }
+
+    fn configure_router(&self, router: Router) -> Router {
+        router.route("/page", web::get(render_page))
+    }
+}
+
+async fn render_page(request: HttpRequest) -> Result<Markup, ErrorPage> {
+    Page::new(request)
+        .with_child(Html::with(|_| html! { p { "hello" } }))
+        .render()
+        .await
+}
+
+// All tests in this file share the same root extension (`TestApp`), since `EXTENSIONS` is a global
+// `OnceLock` initialized only once per test binary (see `core/extension/all.rs`).
+
+// **< Static assets >******************************************************************************
+
+#[pagetop::test]
+async fn htmx_script_is_served_at_the_expected_static_path() {
+    let app = web::test::init_router(Application::prepare(&TestApp).await.test());
+
+    let req = web::test::TestRequest::get()
+        .uri("/htmx/js/htmx.min.js")
+        .to_request();
+    let resp = web::test::send_request(&app, req).await;
+
+    assert_eq!(resp.status(), web::http::StatusCode::OK);
+
+    let body = web::test::read_body_text(resp).await;
+    assert!(!body.is_empty());
+    assert!(body.contains("htmx"));
+}
+
+// **< Automatic script injection (BeforeRenderBody) >***********************************************
+
+#[pagetop::test]
+async fn rendered_pages_automatically_include_the_pinned_htmx_script_tag() {
+    let app = web::test::init_router(Application::prepare(&TestApp).await.test());
+
+    let req = web::test::TestRequest::get().uri("/page").to_request();
+    let resp = web::test::send_request(&app, req).await;
+
+    assert_eq!(resp.status(), web::http::StatusCode::OK);
+
+    let body = web::test::read_body_text(resp).await;
+    // The version must stay in sync with the bundled `assets/js/htmx.min.js`; a mismatch here
+    // would mean the browser caches a stale script under a version tag that no longer matches it.
+    assert!(body.contains(r#"src="/htmx/js/htmx.min.js?v=2.0.10""#));
+    assert!(body.contains("defer"));
+    assert!(body.contains("<p>hello</p>"));
+}