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>

css/pages/_home.css

@@ -264,6 +264,14 @@
     gap: 12px;
 }
 
+/* Tablist wrapper — holds only the tabs (the CTA sits outside it so the
+   role="tablist" contains only role="tab" children, per ARIA). */
+.activities-tabs {
+    display: flex;
+    flex-direction: column;
+    gap: 12px;
+}
+
 /* Tab buttons — card style with icon + active highlight */
 .activity-tab {
     display: flex;
@@ -780,6 +788,9 @@
         width: 100%;
         gap: 10px;
     }
+    .activities-tabs {
+        gap: 10px;
+    }
     .activity-tab {
         padding: 14px 16px;
         gap: 14px;