feat(seo): add Google Preferred Sources button + footer link

New self-contained preferred-source.js (referenced site-wide via
seo_inject GA_LINES):
- small "Add us on Google" text link in the footer (.legal-links) on
  every page, trilingual, using the domain deeplink;
- Google's official interactive pill (publisher.js) on the homepage,
  News hub and Blog hub only, localized (en/mk/sl).
Lets readers mark MSOS as a preferred source (Top Stories / Discover /
News / AI surfaces). Cache-bust bump included.

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

preferred-source.js

@@ -0,0 +1,64 @@
+/* MSOS — "Add as a preferred source on Google".
+ * (1) A small text link in the footer (.legal-links) on every page.
+ * (2) An interactive pill button on the homepage, News hub and Blog hub
+ *     (Google's official button via publisher.js; renders any element with
+ *     the google-add-preferred-source-btn attribute).
+ * Self-contained, no dependencies. Domain-level deeplink works everywhere;
+ * the pill needs Google's library, loaded only on the hub pages.  */
+(function () {
+  var DEEPLINK = 'https://www.google.com/preferences/source?q=msosorg.com';
+
+  var docLang = (document.documentElement.getAttribute('lang') || 'en').toLowerCase();
+  var lang = docLang === 'sl' ? 'si' : (['en', 'mk', 'si'].indexOf(docLang) === -1 ? 'en' : docLang);
+  var btnLang = lang === 'si' ? 'sl' : lang; // Google button uses ISO code (sl)
+
+  var L = {
+    en: { footer: 'Add us on Google', full: 'Add MSOS as a preferred source on Google' },
+    mk: { footer: 'Додади нè на Google', full: 'Додади нè како префериран извор на Google' },
+    si: { footer: 'Dodaj nas na Google', full: 'Dodajte nas kot prednostni vir na Googlu' }
+  }[lang];
+
+  // (1) Footer link — appended once into .legal-links.
+  function addFooterLink() {
+    var box = document.querySelector('.legal-links');
+    if (!box || box.querySelector('.js-preferred-source')) return;
+    var a = document.createElement('a');
+    a.className = 'js-preferred-source';
+    a.href = DEEPLINK;
+    a.target = '_blank';
+    a.rel = 'noopener';
+    a.title = L.full;
+    a.textContent = L.footer;
+    box.appendChild(a);
+  }
+
+  // (2) Interactive pill — only on homepage / news hub / blog hub.
+  function isHub() {
+    var p = location.pathname;
+    if (p.charAt(p.length - 1) !== '/') p += '/';
+    return /^\/(en|mk|si)\/$/.test(p) || /^\/(en|mk|si)\/(news|blog)\/$/.test(p);
+  }
+
+  function addPill() {
+    if (!isHub() || document.getElementById('msos-prefsrc')) return;
+    var anchor = document.querySelector('main h1') || document.querySelector('h1');
+    if (!anchor) return;
+    var wrap = document.createElement('div');
+    wrap.id = 'msos-prefsrc';
+    wrap.className = 'msos-prefsrc';
+    wrap.style.margin = '14px 0 4px';
+    var btn = document.createElement('div');
+    btn.setAttribute('google-add-preferred-source-btn', '');
+    btn.setAttribute('data-lang', btnLang);
+    wrap.appendChild(btn);
+    anchor.insertAdjacentElement('afterend', wrap);
+    var s = document.createElement('script');
+    s.async = true;
+    s.src = 'https://news.google.com/swg/js/v1/publisher.js';
+    document.head.appendChild(s);
+  }
+
+  function init() { addFooterLink(); addPill(); }
+  if (document.readyState === 'loading') document.addEventListener('DOMContentLoaded', init);
+  else init();
+})();