Add Gruperly logotype and favicon from brand assets

Copy logotipo and isotipo assets to src/assets, expose them via
Eleventy passthrough, use the adaptive iso favicon in the head, and
replace the generic placeholder icons in header, footer and demo sidebar.

src/_includes/layouts/base.njk

@@ -5,6 +5,9 @@
   <meta name="viewport" content="width=device-width, initial-scale=1.0" />
   <title>{{ title or site.name }}</title>
   <meta name="description" content="{{ description or site.description }}" />
+  <link rel="icon" type="image/svg+xml" href="/assets/favicon.svg" />
+  <link rel="icon" type="image/png" sizes="512x512" href="/assets/isotipo-y-organica-preview.png" />
+  <link rel="apple-touch-icon" href="/assets/isotipo-y-organica-preview.png" />
   <script>
     if (localStorage.getItem('theme') === 'dark' || (!localStorage.getItem('theme') && window.matchMedia('(prefers-color-scheme: dark)').matches)) {
       document.documentElement.classList.add('dark');