✨ (base): Añade componentes Nav y Navbar

Dropdown incorpora tamaño y estilo de botón configurables
(`button::Size`/`Style`), reutilizados también por Navbar. El tema Basic
sirve `basic.min.css` y añade el JS de inicialización de Navbar.

examples/basic-navbar.rs

@@ -0,0 +1,55 @@
+use pagetop::prelude::*;
+
+include_locales!(LOC from "examples/locale");
+
+struct NavbarDemo;
+
+#[async_trait]
+impl Extension for NavbarDemo {
+    fn dependencies(&self) -> Vec<ExtensionRef> {
+        vec![
+            &pagetop_bootsier::Bootsier,
+            &pagetop::base::extension::Welcome,
+        ]
+    }
+
+    async fn initialize(&self) {
+        let brand = Brand::new()
+            .with_image(image::Source::logo(PageTopSvg::Color))
+            .with_title(Lc::n("PageTop"))
+            .with_route(Route::from("/"));
+
+        let main_nav = Nav::new()
+            .with_item(nav::Item::link(Lc::t("navbar_home", &LOC), "/"))
+            .with_item(nav::Item::link_blank(
+                Lc::t("navbar_docs", &LOC),
+                "https://docs.rs/pagetop",
+            ))
+            .with_item(nav::Item::dropdown(
+                Dropdown::new()
+                    .with_title(Lc::t("navbar_tools", &LOC))
+                    .with_item(dropdown::Item::link(
+                        Lc::t("navbar_generator", &LOC),
+                        "/tools/gen",
+                    ))
+                    .with_item(dropdown::Item::link(
+                        Lc::t("navbar_reports", &LOC),
+                        "/tools/reports",
+                    )),
+            ))
+            .with_item(nav::Item::link(Lc::t("navbar_active", &LOC), "/active").with_active(true))
+            .with_item(nav::Item::link_disabled(
+                Lc::t("navbar_disabled", &LOC),
+                "#",
+            ));
+
+        let navbar = Navbar::brand_left(brand).with_item(navbar::Item::nav(main_nav));
+
+        InRegion::Global(&CoreRegions::Header).add(navbar);
+    }
+}
+
+#[pagetop::main]
+async fn main() -> std::io::Result<()> {
+    Application::prepare(&NavbarDemo).await.run().await
+}