feat(blog): add /blog routes with dedicated editorial layout

app/blog/page.tsx

@@ -0,0 +1,30 @@
+import { getPosts } from '@/lib/posts'
+import { PostSearch } from '@/components/posts/PostSearch'
+
+export const metadata = { title: 'Field Notes' }
+
+export default async function PostsPage() {
+  const posts = await getPosts()
+
+  return (
+    <>
+      <header className="mb-10 border-b border-border pb-8">
+        <h1 className="heading-xl m-0 text-ink">
+          Posts
+        </h1>
+      </header>
+
+      {posts.length > 0 ? (
+        <PostSearch posts={posts} />
+      ) : (
+        <section className="empty-state" aria-label="No posts published">
+          <p className="font-mono text-xs uppercase tracking-[0.22em] text-ink-soft">No posts yet</p>
+          <h2 className="heading-sm m-0 text-ink">The archive is empty.</h2>
+          <p className="m-0 max-w-xl text-sm leading-6 text-ink-soft">
+            Publish an MDX post to populate this list and enable archive search.
+          </p>
+        </section>
+      )}
+    </>
+  )
+}