Build landing page from Penpot design, with multi-language switcher

Implement the "Desktop dark" Penpot design: nav, hero, about, products
teaser and contact form, with the exported logo and wave artwork and
self-hosted Poppins, Roboto Flex and Chillax fonts.

- Shared page markup in _includes/home.pug; copy in locales/{en,pl}.json
- Footer language switcher and hreflang tags generated from the locales
- Contact form composes a mailto: to the address in _data/site.json
- Stacked layout below 1024px

tailwind.config.js

@@ -1,7 +1,18 @@
 module.exports = {
   content: ["./src/**/*.pug"],
   theme: {
-    extend: {},
+    extend: {
+      colors: {
+        accent: "#5272d3",
+        deep: "#15164e",
+        "accent-light": "#748bd7",
+      },
+      fontFamily: {
+        poppins: ["Poppins", "sans-serif"],
+        "roboto-flex": ['"Roboto Flex"', "sans-serif"],
+        chillax: ["Chillax", "sans-serif"],
+      },
+    },
   },
   plugins: [],
 };