Full-site nav: one auth-aware nav bar on every page

- SiteHeader: a single consistent main nav (Home, News, Screenshots, Five on
  Friday, Newsletter, Wiki, Shard, About) with active-state highlighting, plus
  an auth-aware entry on the right — Sign in when logged out, My Account
  (player) or Admin (staff) when logged in.
- Portal (landing) now renders the site header too, so the nav is present
  across the entire site, not just interior pages.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_011qPmpmVH1xGCiZoz9m9vW3

client/src/routes/public/Portal.jsx

@@ -40,7 +40,7 @@ export default function Portal() {
   const elements = [...layout.elements].sort((a, b) => (a.z || 0) - (b.z || 0))
 
   return (
-    <PublicLayout header={false}>
+    <PublicLayout>
       <main style={{ minHeight: '100vh', display: 'flex', flexDirection: 'column' }}>
         {PREVIEW && draft && (
           <div