feat: scaffold Astro project with en/fr i18n routing

Sets output to static (Astro default) with path-based i18n routing
(/en/, /fr/) and no unprefixed default-locale route, per the hub
landing page design spec.

astro.config.mjs

@@ -0,0 +1,12 @@
+import { defineConfig } from 'astro/config';
+
+export default defineConfig({
+  site: 'https://www.ombrora.com',
+  i18n: {
+    locales: ['en', 'fr'],
+    defaultLocale: 'en',
+    routing: {
+      prefixDefaultLocale: true,
+    },
+  },
+});