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/app/layout.tsx

@@ -1,5 +1,7 @@
 import type { Metadata } from "next";
 import type { ReactNode } from "react";
+import { SiteNav } from "@/components/site-nav";
+import "./globals.css";
 
 export const metadata: Metadata = {
   title: "AtomCMS",
@@ -9,7 +11,10 @@ export const metadata: Metadata = {
 export default function RootLayout({ children }: { children: ReactNode }) {
   return (
     <html lang="en">
-      <body>{children}</body>
+      <body>
+        <SiteNav />
+        <div className="container">{children}</div>
+      </body>
     </html>
   );
 }