feat: UI polish — AI enhancements branding, footer year, admin background fix

- Header: add "+ AI enhancements" italic subtitle below logo
- Footer: update copyright year to 2021–current, add "AI enhancements by Cloud Host" link
- Admin page: wrap all states in pageBg Box so dark-mode background shows correctly

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

components/Footer.tsx

@@ -20,12 +20,16 @@ const Footer: FC<Props> = (props) => (
         {...props}
     >
         <Link href="https://github.com/thedaviddelta/lingva-translate/blob/main/LICENSE" isExternal={true}>
-            <Text as="span">&#169; 2021 thedaviddelta & contributors</Text>
+            <Text as="span">&#169; 2021–{new Date().getFullYear()} thedaviddelta & contributors</Text>
         </Link>
         <Text as="span" display={["none", null, "unset"]}>·</Text>
         <Link href="https://www.gnu.org/licenses/agpl-3.0.html" isExternal={true}>
             <Text as="span">Licensed under AGPLv3</Text>
         </Link>
+        <Text as="span" display={["none", null, "unset"]}>·</Text>
+        <Link href="https://cloudhost.es" isExternal={true}>
+            <Text as="span">AI enhancements by Cloud Host</Text>
+        </Link>
         {vercelSponsor && (
             <>
                 <Text as="span" display={["none", null, "unset"]}>·</Text>