fix: replace hardcoded site name with dynamic settings

- Add public /api/settings endpoint (force-dynamic, no auth) exposing
  site_name, site_description, footer_copyright, footer_links
- Navbar, login, register pages fetch site_name via useEffect
- Homepage hero and footer read site_name and site_description from DB
- Fix admin settings form silently ignoring API errors on save

app/src/components/storefront/Navbar.tsx

@@ -7,6 +7,7 @@ import { useUser } from '@/context/UserContext'
 
 export function Navbar() {
   const [cartCount, setCartCount] = useState(0)
+  const [siteName, setSiteName] = useState('ShopX')
   const { user, refreshUser } = useUser()
   const router = useRouter()
 
@@ -16,6 +17,16 @@ export function Navbar() {
     setCartCount(count)
   }, [])
 
+  useEffect(() => {
+    fetch('/api/settings')
+      .then((r) => r.json())
+      .then((data) => {
+        const name = data.settings?.site_name
+        if (name) setSiteName(name as string)
+      })
+      .catch(() => {})
+  }, [])
+
   async function handleLogout() {
     await fetch('/api/auth/logout', { method: 'POST' })
     await refreshUser()
@@ -28,7 +39,7 @@ export function Navbar() {
       <div className="max-w-7xl mx-auto px-4 sm:px-6 lg:px-8">
         <div className="flex items-center justify-between h-16">
           <Link href="/" className="text-xl font-bold text-gray-900">
-            ShopX
+            {siteName}
           </Link>
 
           <nav className="flex items-center gap-6 text-sm">