feat: implement functional slider with Swiper.js

- Add Swiper.js via CDN for carousel functionality
- Restructure excerpts section: 6 individual slides instead of 2 grouped slides
- Implement responsive behavior: 3 slides per view on desktop, 1 on mobile
- Add infinite loop navigation with prev/next buttons and pagination bullets
- Create custom styles in _section_4-excerpts.scss (no Swiper CSS)
- Add script.js with Swiper configuration and responsive breakpoints

Co-Authored-By: Claude Sonnet 4.5 <noreply@anthropic.com>

assets/js/script.js

@@ -0,0 +1,44 @@
+document.addEventListener('DOMContentLoaded', function() {
+  const excerptSwiper = new Swiper('.excerpts-swiper', {
+    // Slides visibles et groupement
+    slidesPerView: 3,
+    slidesPerGroup: 3,
+    spaceBetween: 30,
+
+    // Infinite loop
+    loop: true,
+
+    // Navigation arrows
+    navigation: {
+      nextEl: '.swiper-button-next',
+      prevEl: '.swiper-button-prev',
+    },
+
+    // Pagination bullets
+    pagination: {
+      el: '.swiper-pagination',
+      clickable: true,
+      dynamicBullets: false,
+    },
+
+    // Transitions
+    speed: 400,
+    effect: 'slide',
+
+    // Responsive breakpoints
+    breakpoints: {
+      // Mobile : <= 768px
+      0: {
+        slidesPerView: 1,
+        slidesPerGroup: 1,
+        spaceBetween: 20,
+      },
+      // Desktop : > 768px
+      769: {
+        slidesPerView: 3,
+        slidesPerGroup: 3,
+        spaceBetween: 30,
+      }
+    }
+  });
+});