feat(loyalty): translatable categories + mandatory on earn points

- Add name_translations JSON column to StoreTransactionCategory
  (migration loyalty_008). Stores {"en": "Men", "fr": "Hommes", ...}.
  Model has get_translated_name(lang) helper.
- Admin CRUD form now has FR/DE/LB translation inputs alongside the
  default name.
- Points earn: category_id is now mandatory when the store has
  active categories configured. Returns CATEGORY_REQUIRED error.
- Stamps: category remains optional (quick tap workflow).

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

app/modules/loyalty/static/admin/js/loyalty-merchant-detail.js

@@ -38,6 +38,7 @@ function adminLoyaltyMerchantDetail() {
         storeCategories: [],
         showAddCategory: false,
         newCategoryName: '',
+        newCategoryTranslations: { fr: '', de: '', lb: '' },
 
         // State
         loading: false,
@@ -284,11 +285,20 @@ function adminLoyaltyMerchantDetail() {
         async createCategory() {
             if (!this.newCategoryName || !this.selectedCategoryStoreId) return;
             try {
+                // Build translations dict (only include non-empty values)
+                const translations = {};
+                if (this.newCategoryName) translations.en = this.newCategoryName;
+                for (const [lang, val] of Object.entries(this.newCategoryTranslations)) {
+                    if (val) translations[lang] = val;
+                }
+
                 await apiClient.post(`/admin/loyalty/stores/${this.selectedCategoryStoreId}/categories`, {
                     name: this.newCategoryName,
+                    name_translations: Object.keys(translations).length > 0 ? translations : null,
                     display_order: this.storeCategories.length,
                 });
                 this.newCategoryName = '';
+                this.newCategoryTranslations = { fr: '', de: '', lb: '' };
                 this.showAddCategory = false;
                 await this.loadCategoriesForStore();
                 Utils.showToast('Category created', 'success');