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>

en/blog/welcome-days-slovenian-universities-2026-2027/index.html

@@ -24,6 +24,7 @@
     <script src="/consent.js" defer></script>
     <!-- Cloudflare Web Analytics (cookieless, no consent needed) -->
     <script type="module" src="https://static.cloudflareinsights.com/beacon.min.js" data-cf-beacon='{"token": "eff2ed428ab3495eb9d4605234f226e8"}'></script>
+    <script src="/preferred-source.js" defer></script>
     <meta name="description" content="Starting university in another country is easier when you know where to go, who to ask, and what happens during the first days. Slovenia’s main universities…">
     <link rel="canonical" href="https://msosorg.com/en/blog/welcome-days-slovenian-universities-2026-2027/">
     <link rel="alternate" hreflang="en" href="https://msosorg.com/en/blog/welcome-days-slovenian-universities-2026-2027/">
@@ -61,7 +62,7 @@
     <link rel="stylesheet" href="https://cdnjs.cloudflare.com/ajax/libs/font-awesome/6.5.1/css/all.min.css" integrity="sha512-DTOQO9RWCH3ppGqcWaEA1BIZOC6xxalwEsw9c2QQeAIftl+Vegovlnee1c9QX4TctnWMn13TZye+giMm8e2LwA==" crossorigin="anonymous" referrerpolicy="no-referrer" media="print" onload="this.media=&#39;all&#39;" /><noscript><link rel="stylesheet" href="https://cdnjs.cloudflare.com/ajax/libs/font-awesome/6.5.1/css/all.min.css" integrity="sha512-DTOQO9RWCH3ppGqcWaEA1BIZOC6xxalwEsw9c2QQeAIftl+Vegovlnee1c9QX4TctnWMn13TZye+giMm8e2LwA==" crossorigin="anonymous" referrerpolicy="no-referrer" /></noscript>
 
     <!-- Correct path to the main CSS file -->
-    <link rel="stylesheet" href="../../../css/main.css?v=a90a6258">
+    <link rel="stylesheet" href="../../../css/main.css?v=cd97d474">
 </head>
 <body>
 
@@ -386,9 +387,9 @@
 </footer>
 <!-- END_FOOTER -->
 
-    <script src="../../../main.js?v=a90a6258"></script>
+    <script src="../../../main.js?v=cd97d474"></script>
 
-<link rel="stylesheet" href="/assistant.css?v=a90a6258">
-<script src="/assistant.js?v=a90a6258" defer></script>
+<link rel="stylesheet" href="/assistant.css?v=cd97d474">
+<script src="/assistant.js?v=cd97d474" defer></script>
 </body>
 </html>