Add GDPR cookie-consent banner (Consent Mode v2)

- consent.js: self-contained, non-blocking bottom banner in EN/MK/SI,
  remembers the choice in localStorage, links to the per-language cookie
  policy. Accept -> gtag consent 'update' granted; Decline stays denied.
- Head GA snippet restores a returning visitor's prior "granted" choice
  before the first hit; loads /consent.js on every page.
- Re-openable via window.msosOpenConsent() for a "manage cookies" link.

Verified in-browser: shows for new visitors, Accept grants + remembers,
reload keeps consent without re-prompting, Slovene text + /si/ policy link.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

en/student-welcome-guide/index.html

@@ -14,9 +14,14 @@
         ad_storage: 'denied', ad_user_data: 'denied', ad_personalization: 'denied',
         analytics_storage: 'denied', wait_for_update: 500
       });
+      // Restore a returning visitor's prior choice before the first hit.
+      try { if (localStorage.getItem('msos-consent') === 'granted') {
+        gtag('consent', 'update', { ad_storage:'granted', ad_user_data:'granted',
+          ad_personalization:'granted', analytics_storage:'granted' }); } } catch(e){}
       gtag('js', new Date());
       gtag('config', 'G-WVYV807VSS');
     </script>
+    <script src="/consent.js" defer></script>
     <meta name="description" content="Your complete route from a Macedonian secondary school or first degree to enrolled student life in Slovenia.">
     <link rel="canonical" href="https://msosorg.com/en/student-welcome-guide/">
     <link rel="alternate" hreflang="en" href="https://msosorg.com/en/student-welcome-guide/">