feat: bootstrap foundation application

apps/web/src/app.tsx

@@ -0,0 +1,31 @@
+export function App() {
+  return (
+    <main class="shell">
+      <section class="hero">
+        <p class="eyebrow">MD Hub Secure</p>
+        <h1>Preact foundation for future hydrated features</h1>
+        <p class="lede">
+          The Go server is the source of truth for rendering document pages.
+          This app is the scaffold for search, sync, comments, and design
+          tooling that will hydrate over time.
+        </p>
+      </section>
+
+      <section class="grid">
+        <article class="card">
+          <h2>Current scope</h2>
+          <p>
+            Routing, bundling, TypeScript, and styles are in place for later
+            feature islands.
+          </p>
+        </article>
+        <article class="card">
+          <h2>Next milestone</h2>
+          <p>
+            Sync protocol UI, offline cache status, and browser-side search.
+          </p>
+        </article>
+      </section>
+    </main>
+  );
+}