fix(menu-app): crash when tagline/hours fields are null

The API now always sends restaurant.tagline/blurb as {en, gr} objects,
including when a site hasn't set them yet (both null). The old
`?? r.tagline` fallback rendered the whole object as a React child in
that case (React error #31) instead of falling back to a display
string. Fall back to the localized fallback string instead.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>

connect_frontend/menu-app/src/pages/MenuPage.jsx

@@ -12,7 +12,7 @@ import {
   eur, discountedPrice, discountPct,
 } from '../components/primitives'
 
-// TODO: Replace with real data from API once backend includes restaurant info
+// Used when a site hasn't configured a field yet (API sends nulls until set in sysadmin)
 const RESTAURANT_FALLBACK = {
   name: 'Our Menu',
   tagline: { en: 'Kitchen & Bar', gr: 'Κουζίνα & Μπαρ' },
@@ -160,7 +160,7 @@ function Hero({ lang, setLang, restaurant }) {
         </h1>
       )}
       <div className="mt-1.5 font-sans text-[14px] font-medium uppercase tracking-[0.18em] text-[#9caf88]">
-        {r.tagline?.[lang] ?? r.tagline ?? ''}
+        {r.tagline?.[lang] || RESTAURANT_FALLBACK.tagline[lang] || ''}
       </div>
 
       {/* Ornament */}
@@ -171,7 +171,7 @@ function Hero({ lang, setLang, restaurant }) {
       </div>
 
       <p className="mx-auto max-w-[300px] text-[13px] leading-relaxed text-[#7d7660]">
-        {r.blurb?.[lang] ?? r.blurb ?? ''}
+        {r.blurb?.[lang] || RESTAURANT_FALLBACK.blurb[lang] || ''}
       </p>
 
       {r.hours?.[lang] && (