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)/blog/[slug]/page.tsx

@@ -0,0 +1,40 @@
+import { notFound } from "next/navigation";
+import { TopBar, BackLink, InfoLink } from "../../../../components/shell/TopBar";
+import { getPostBySlug } from "../../../../lib/posts";
+
+type PageProps = {
+    params: Promise<{
+        slug: string;
+    }>;
+};
+
+export default async function BlogPostPage({ params }: PageProps) {
+    const { slug } = await params;
+
+    const post = getPostBySlug(slug);
+    if (!post) return notFound();
+
+    return (
+        <div>
+            <TopBar
+                title={post.meta.title}
+                left={<BackLink href="/blog" />}
+                right={<InfoLink href="/about" />}
+            />
+
+            <main className="mx-auto max-w-3xl px-4 py-10">
+                <div className="text-xs opacity-70">
+                    {post.meta.date}
+                </div>
+
+                <h1 className="mt-2 text-2xl font-semibold">
+                    {post.meta.title}
+                </h1>
+
+                <div className="mt-8 whitespace-pre-wrap leading-relaxed">
+                    {post.content}
+                </div>
+            </main>
+        </div>
+    );
+}