docs: add minimalist UI design spec

Covers Tailwind CSS setup, dark mode via next-themes, flag image language
switcher, SEO metadata + JSON-LD, and full layout for home and status pages.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

src/app/page.tsx

@@ -0,0 +1,10 @@
+import { SubmitForm } from '@/components/SubmitForm'
+
+export default function Home() {
+  return (
+    <main style={{ padding: '2rem' }}>
+      <h1>Ombrora</h1>
+      <SubmitForm />
+    </main>
+  )
+}