Fix API paths and make hotel name configurable

- /api/notices → /notices/api/notices to match nginx location block
  (was returning portal index.html causing JSON parse error)
- Add VITE_HOTEL_NAME build arg, remove hardcoded hotel name
- Add vite-env.d.ts for TypeScript import.meta.env support

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

frontend/src/components/AuthGate.tsx

@@ -85,7 +85,7 @@ export function AuthGate({ children }: Props) {
             Noticeboard
           </h1>
           <p style={{ color: 'var(--text-muted)', fontSize: '0.875rem', marginBottom: '1.5rem' }}>
-            Hotel Number Four
+            {import.meta.env.VITE_HOTEL_NAME}
           </p>
           <form onSubmit={login} style={{ display: 'flex', flexDirection: 'column', gap: '0.75rem' }}>
             <input