Make hotel name configurable via VITE_HOTEL_NAME build arg

Defaults to 'Number Four at Stow'. Replaces hardcoded 'Hotel Number Four'
and 'HNF Manage' in sidebar, login page, and browser title. Other hotels
set VITE_HOTEL_NAME in their /opt/portal/.env before rebuilding.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

src/components/Sidebar.tsx

@@ -20,10 +20,10 @@ export function Sidebar({ user, activeSlug }: Props) {
     }}>
       <div style={{ padding: '1.25rem 1rem 1rem', borderBottom: '1px solid var(--surface-2)' }}>
         <div style={{ color: 'var(--gold)', fontWeight: 700, fontSize: '0.9rem', letterSpacing: '0.05em' }}>
-          HNF MANAGE
+          MANAGE
         </div>
         <div style={{ color: 'var(--text-muted)', fontSize: '0.75rem', marginTop: '0.2rem' }}>
-          Hotel Number Four
+          {import.meta.env.VITE_HOTEL_NAME}
         </div>
       </div>