fix(categories): strip diacritics from auto-generated slugs

Accented chars (ã, ç, é, etc.) were silently dropped by the slug
regex because \w only matches ASCII. NFD decomposition + combining
mark removal converts them to ASCII equivalents instead.

Co-Authored-By: Claude Sonnet 4.6 <[email protected]>

backend/src/routes/adminCategories.js

@@ -56,7 +56,9 @@ router.post('/', adminAuth, requirePermission('settings.edit'), [
     const { name, slug, is_global = true, event_id = null } = req.body;
     
     // Generate slug if not provided
-    const categorySlug = slug || name.toLowerCase()
+    const categorySlug = slug || name
+      .normalize('NFD').replace(/[̀-ͯ]/g, '')
+      .toLowerCase()
       .replace(/[^\w\s-]/g, '')
       .replace(/\s+/g, '-')
       .replace(/-+/g, '-')
@@ -128,7 +130,9 @@ router.put('/:id', adminAuth, requirePermission('settings.edit'), [
 
     const updateData = {
       name,
-      slug: name.toLowerCase()
+      slug: name
+        .normalize('NFD').replace(/[̀-ͯ]/g, '')
+        .toLowerCase()
         .replace(/[^\w\s-]/g, '')
         .replace(/\s+/g, '-')
         .replace(/-+/g, '-')