Add media carousel section to homepage

Display past event photos in an auto-playing carousel between the
"What is Spanglish?" and "Stay Updated" sections. Images are loaded
dynamically from /images/carrousel/ folder with support for jpg, png,
and webp formats.

frontend/src/i18n/locales/en.json

@@ -53,6 +53,13 @@
     "gallery": {
       "title": "Our Community"
     },
+    "carousel": {
+      "title": "Moments from past events",
+      "subtitle": "A glimpse of our language exchange meetups",
+      "cta": "See upcoming events",
+      "previous": "Previous image",
+      "next": "Next image"
+    },
     "newsletter": {
       "title": "Stay Updated",
       "description": "Subscribe to get notified about upcoming events",