Nav cleanup + new Blog page

Remove 'Mentorship Programme' and 'Open calls' from the menus, rename 'Announcements' to 'News and Announcements', and wire the Blog link. Add a trilingual /<lang>/blog/ page with a distinct look: featured strip, client-side topic filters, and a masonry card wall with colour-coded tags (placeholder posts for now).

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

blog-filter.js

@@ -0,0 +1,22 @@
+/* Blog topic filter: chips toggle which cards are shown. No dependencies. */
+(function () {
+    var list = document.querySelector('.blog-list');
+    if (!list) return;
+    var chips = list.querySelectorAll('.blog-chip');
+    var cards = list.querySelectorAll('.blog-card');
+
+    function apply(topic) {
+        cards.forEach(function (card) {
+            var show = topic === 'all' || card.getAttribute('data-topic') === topic;
+            card.hidden = !show;
+        });
+    }
+
+    chips.forEach(function (chip) {
+        chip.addEventListener('click', function () {
+            chips.forEach(function (c) { c.classList.remove('is-active'); });
+            chip.classList.add('is-active');
+            apply(chip.getAttribute('data-topic'));
+        });
+    });
+})();