Remove "Get Involved" nav dropdown + full-width header alignment

- Remove the "Get Involved" dropdown (Become a member / Support MSOS): dead
  href="#" links that duplicated the top-right buttons. Swept site-wide
  (desktop + mobile, en/si/mk) - 390 blocks across 195 pages, including the
  privacy-policy header the generators slice from, so regeneration stays clean.
  Nav is now Who We Are / What We Do / For Students / News + the two buttons.
- Header now spans the full page width: logo + text menus flush left, buttons +
  language switcher flush right (was constrained to a centred 1280px container,
  which left the logo floating inward on wide screens). CSS-only in _header.css,
  scoped so the mobile hamburger layout is unchanged.

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

css/layout/_header.css

@@ -28,6 +28,24 @@
     z-index: 1000;
 }
 
+/* Header spans the full page width: logo + menus flush left, buttons +
+   language flush right. Overrides the shared .container 1280px centering
+   for the header only (page content elsewhere stays centered). */
+.dropdown-header-navigation .container {
+    max-width: none;
+    padding: 0 40px;
+}
+@media (max-width: 768px) {
+    .dropdown-header-navigation .container { padding: 0 20px; }
+}
+/* Desktop split: the right-wrapper fills the row so the menus sit next to the
+   logo on the left, and the buttons + language get pushed to the far right. */
+@media (min-width: 1025px) {
+    .dropdown-header-navigation .header-right-wrapper { flex: 1; }
+    .dropdown-header-navigation .header-right-wrapper > nav { margin-left: 40px; }
+    .dropdown-header-navigation .navigation-actions { margin-left: auto; }
+}
+
 /* 2. Vsebina glave (logotip, navigacija) - POSODOBLJENO */
 .logo-link .logo-img {
     height: 32px;