Add a blog, built from pages

A post is a page in the panel's "Blog" category, so it is written,
translated, scheduled and reviewed like any page, and the MCP server
can publish one the same way. Nothing new in the API.

- /blog (/en/blog, /ca/blog): posts newest first, with image, date and
  excerpt.
- A post shows its date and leads back to the blog; its structured data
  is a BlogPosting.
- /blog/rss.xml?lang=xx: one feed per language, announced in <head>.
- Posts stay out of the header and the footer, which links the blog
  once there is any post instead of growing with every one.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

tools/mock-api.mjs

@@ -55,7 +55,19 @@ const page = (id, title, slug, featured) => ({
   alternates: { es: `/${slug}`, en: `/en/${slug}-en`, ca: `/ca/${slug}-ca` }, path: `/${slug}`,
 });
 
-const pages = [page(1, 'Sobre nosotros', 'sobre-nosotros', true), page(2, 'Contacto', 'contacto', false)];
+const post = (id, title, slug, published_at) => ({
+  ...page(id, title, slug, false),
+  published_at,
+  excerpt: 'Lo que hemos aprendido este mes, contado sin prisa y con ejemplos de código.',
+  category: { id: 9, name: 'Blog', slug: 'blog', position: 3 },
+});
+
+const pages = [
+  page(1, 'Sobre nosotros', 'sobre-nosotros', true),
+  page(2, 'Contacto', 'contacto', false),
+  post(3, 'Por qué volvimos a renderizar en el servidor', 'volvimos-al-servidor', '2026-09-20T09:00:00Z'),
+  post(4, 'Nuestro primer año como colectivo', 'primer-ano', '2026-06-01T09:00:00Z'),
+];
 
 const data = {
   '/public/v1/pages': pages,
@@ -184,8 +196,14 @@ data['/public/v1/slugs'] = {
 data['/public/v1/redirects'] = [{ from: '/proyectos/catalogo-viejo', to: '/proyectos/catalogo', status: 301, locale: null }];
 
 createServer((req, res) => {
-  const path = new URL(req.url, 'http://x').pathname.replace(/^\/api/, '');
-  const payload = data[path];
+  const url = new URL(req.url, 'http://x');
+  const path = url.pathname.replace(/^\/api/, '');
+  let payload = data[path];
+
+  // The one filter the frontend relies on: pages by category slug.
+  if (path === '/public/v1/pages' && url.searchParams.get('category')) {
+    payload = payload.filter((p) => p.category?.slug === url.searchParams.get('category'));
+  }
 
   res.setHeader('content-type', 'application/json');