Add catalog subject banner feature: Introduce optional header images for subjects in the catalog, update CONTRIBUTING.md with guidelines for adding banners, and modify catalog data structure to support banner URLs. Enhance frontend components and styles to display banners effectively. Update TypeScript types and curriculum structure to accommodate new banner functionality.

frontend/src/components/catalog-app.tsx

@@ -153,7 +153,21 @@ export function CatalogApp() {
       </aside>
 
       <div class="catalog-main">
-        <header class="catalog-header">
+        <header
+          class="catalog-header"
+          classList={{ "catalog-header--has-banner": Boolean(currentSubject().banner) }}
+        >
+          <Show when={currentSubject().banner}>
+            <div class="catalog-header__banner" aria-hidden="true">
+              <img
+                src={currentSubject().banner!}
+                alt=""
+                width={1400}
+                height={700}
+                decoding="async"
+              />
+            </div>
+          </Show>
           <div class="catalog-header__head">
             <div class="catalog-header__intro">
               <h1 class="catalog-header__title">{currentSubject().name}</h1>

frontend/src/main.tsx

@@ -13,6 +13,7 @@ function readConfig() {
       homeUrl: "/",
       browseUrl: "/catalog/",
       aboutUrl: "/about/",
+      faqUrl: "/faq/",
       searchUrl: "/search/",
       contributingUrl: "/contributing/",
       githubUrl: "https://github.com/openfreebooks/openfreebooks",
@@ -23,6 +24,7 @@ function readConfig() {
     homeUrl: string;
     browseUrl: string;
     aboutUrl: string;
+    faqUrl: string;
     searchUrl: string;
     contributingUrl: string;
     githubUrl: string;
@@ -86,6 +88,7 @@ const navLinks = [
   { label: "Browse", href: config.browseUrl },
   { label: "Search", href: config.searchUrl },
   { label: "About", href: config.aboutUrl },
+  { label: "FAQ", href: config.faqUrl },
   { label: "GitHub", href: config.githubUrl },
 ];