Add data-driven public pages (home, news, profile)

Real App Router pages reading the converted Prisma models:
- home: latest 4 articles (websiteArticles) + hotel_name from settings
- /news + /news/[slug]: article index and detail
- /u/[username]: profile (avatar via imager helper, motto, rank, credits, online)
- shared SiteNav (reads session via auth() + hotel_name), globals.css
- src/lib/format.ts: avatarImageUrl + excerpt helpers (unit-tested)

Verified: tsc exit 0, vitest 43/43, next build exit 0 (7 routes). Pages render
against a live DB (deferred until DATABASE_URL is provided). i18n to be layered
on next.

src/components/site-nav.tsx

@@ -0,0 +1,30 @@
+import Link from "next/link";
+import { auth } from "@/lib/auth";
+import { siteSettings } from "@/lib/services/site-settings";
+
+export async function SiteNav() {
+  const [hotelName, session] = await Promise.all([
+    siteSettings.get("hotel_name", "Atom"),
+    auth(),
+  ]);
+
+  return (
+    <nav className="site-nav">
+      <div className="container">
+        <Link href="/" className="brand">
+          {hotelName ?? "Atom"}
+        </Link>
+        <Link href="/news">News</Link>
+        <span className="spacer" />
+        {session?.user ? (
+          <>
+            <Link href={`/u/${session.user.name}`}>{session.user.name}</Link>
+            <Link href="/client">Hotel</Link>
+          </>
+        ) : (
+          <Link href="/login">Login</Link>
+        )}
+      </div>
+    </nav>
+  );
+}