feat(blog): add file-based blog with dynamic slugs, MDX content and layout shell

- Introduced blog routing using Next.js App Router
- Implemented dynamic [slug] pages for blog posts
- Added MDX-based content loading via lib/posts
- Integrated shared TopBar layout with navigation
- Established clear content, lib and component separation

apps/public-web/app/(site)/page.tsx

@@ -0,0 +1,23 @@
+import Link from "next/link";
+import { TopBar, InfoLink } from "../../components/shell/TopBar";
+
+export default function HomePage(){
+    return(
+        <div>
+            <TopBar title="VOYAGE" right={<InfoLink href="/about" />} />
+
+            <main className="mx-auto max-w-3xl px-4 py-10">
+                <h1 className="text-2xl font-semibold">Public Web</h1>
+                <p className="mt-3 opacity-80">
+                    Das ist das Grundgeruest. Von hier aus baust du Design & Content iterativ.
+                </p>
+
+                <div className="mt-6">
+                    <Link className="underline" href="/blog">
+                        Go to Blog
+                    </Link>
+                </div>
+            </main>
+        </div>
+    )
+}