feat(loyalty): transaction categories — admin UI + web terminal

Admin merchant detail page:
- New "Transaction Categories" section with store selector
- Inline add form, activate/deactivate toggle, delete button
- Categories CRUD via /admin/loyalty/stores/{id}/categories API

Web terminal:
- Loads categories on init via /store/loyalty/categories
- Category pill selector shown in PIN modal before stamp/earn actions
- Selected category_id passed to stamp and points API calls
- Categories are optional (selector hidden when none configured)

4 new i18n keys (EN).

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

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

@@ -33,6 +33,12 @@ function adminLoyaltyMerchantDetail() {
         settings: null,
         locations: [],
 
+        // Transaction categories
+        selectedCategoryStoreId: '',
+        storeCategories: [],
+        showAddCategory: false,
+        newCategoryName: '',
+
         // State
         loading: false,
         error: null,
@@ -258,6 +264,59 @@ function adminLoyaltyMerchantDetail() {
         formatNumber(num) {
             if (num === null || num === undefined) return '0';
             return new Intl.NumberFormat('en-US').format(num);
+        },
+
+        // Transaction categories
+        async loadCategoriesForStore() {
+            if (!this.selectedCategoryStoreId) {
+                this.storeCategories = [];
+                return;
+            }
+            try {
+                const response = await apiClient.get(`/admin/loyalty/stores/${this.selectedCategoryStoreId}/categories`);
+                this.storeCategories = response?.categories || [];
+            } catch (error) {
+                loyaltyMerchantDetailLog.warn('Failed to load categories:', error.message);
+                this.storeCategories = [];
+            }
+        },
+
+        async createCategory() {
+            if (!this.newCategoryName || !this.selectedCategoryStoreId) return;
+            try {
+                await apiClient.post(`/admin/loyalty/stores/${this.selectedCategoryStoreId}/categories`, {
+                    name: this.newCategoryName,
+                    display_order: this.storeCategories.length,
+                });
+                this.newCategoryName = '';
+                this.showAddCategory = false;
+                await this.loadCategoriesForStore();
+                Utils.showToast('Category created', 'success');
+            } catch (error) {
+                Utils.showToast(error.message || 'Failed to create category', 'error');
+            }
+        },
+
+        async toggleCategoryActive(cat) {
+            try {
+                await apiClient.patch(`/admin/loyalty/stores/${this.selectedCategoryStoreId}/categories/${cat.id}`, {
+                    is_active: !cat.is_active,
+                });
+                await this.loadCategoriesForStore();
+            } catch (error) {
+                Utils.showToast(error.message || 'Failed to update category', 'error');
+            }
+        },
+
+        async deleteCategory(catId) {
+            if (!confirm('Delete this category?')) return;
+            try {
+                await apiClient.delete(`/admin/loyalty/stores/${this.selectedCategoryStoreId}/categories/${catId}`);
+                await this.loadCategoriesForStore();
+                Utils.showToast('Category deleted', 'success');
+            } catch (error) {
+                Utils.showToast(error.message || 'Failed to delete category', 'error');
+            }
         }
     };
 }