fix(a11y): activities tablist must contain only tabs

The "Become a member" CTA was a direct child of role="tablist", which
violates the ARIA rule that a tablist may only contain role="tab" children
(axe: aria-required-children). Wrap the 4 tabs in an inner
.activities-tabs[role=tablist] and leave the CTA as a sibling; add matching
flex CSS so the layout is unchanged. JS uses `.activities-nav .activity-tab`
(descendant), so tab behavior is unaffected. EN/MK/SI. Cache-bust bump.

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

en/student-welcome-guide/bachelor-application/index.html

@@ -62,7 +62,7 @@
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     <!-- Correct path to the main CSS file -->
-    <link rel="stylesheet" href="../../../css/main.css?v=cd97d474">
+    <link rel="stylesheet" href="../../../css/main.css?v=54203d0c">
 </head>
 <body>
 
@@ -394,9 +394,9 @@
 </footer>
 <!-- END_FOOTER -->
 
-    <script src="../../../main.js?v=cd97d474"></script>
-    <script src="../../../guide-feedback.js?v=cd97d474"></script>
-<link rel="stylesheet" href="/assistant.css?v=cd97d474">
-<script src="/assistant.js?v=cd97d474" defer></script>
+    <script src="../../../main.js?v=54203d0c"></script>
+    <script src="../../../guide-feedback.js?v=54203d0c"></script>
+<link rel="stylesheet" href="/assistant.css?v=54203d0c">
+<script src="/assistant.js?v=54203d0c" defer></script>
 </body>
 </html>