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/page.tsx

@@ -0,0 +1,44 @@
+import Link from "next/link";
+import { TopBar, BackLink, InfoLink } from "../../../components/shell/TopBar";
+import { getAllPosts } from "../../../lib/posts";
+
+export default function BlogIndexPage() {
+    const posts = getAllPosts();
+
+    return (
+        <div>
+            <TopBar
+                title="Blog"
+                left={<BackLink href="/" />}
+                right={<InfoLink href="/about" />}
+            />
+
+            <main className="mx-auto max-w-3xl px-4 py-10">
+                <div className="space-y-6">
+                    {posts.map((p) => (
+                        <article
+                            key={p.slug}
+                            className="border border-black/10 p-4"
+                        >
+                            <div className="text-xs opacity-70">
+                                {p.meta.date}
+                            </div>
+
+                            <h2 className="text-lg font-semibold">
+                                <Link href={`/blog/${p.slug}`}>
+                                    {p.meta.title}
+                                </Link>
+                            </h2>
+
+                            {p.meta.excerpt ? (
+                                <p className="mt-2 opacity-80">
+                                    {p.meta.excerpt}
+                                </p>
+                            ) : null}
+                        </article>
+                    ))}
+                </div>
+            </main>
+        </div>
+    );
+}