feat(loyalty): multi-select categories on transactions

Switch from single category_id to category_ids JSON array on
transactions. Sellers can now select multiple categories (e.g.,
Men + Accessories) when entering stamp/points transactions.

- Migration loyalty_009: drop category_id FK, add category_ids JSON
- Schemas: category_id → category_ids (list[int] | None)
- Services: stamp_service + points_service accept category_ids
- Terminal UI: pills are now multi-select (toggle on/off)
- Transaction response: category_names (list[str]) resolved from IDs
- Recent transactions table: new Category column showing comma-
  separated names

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

app/modules/loyalty/templates/loyalty/store/terminal.html

@@ -286,13 +286,14 @@
                         <th class="px-4 py-3">{{ _('loyalty.store.terminal.col_customer') }}</th>
                         <th class="px-4 py-3">{{ _('loyalty.store.terminal.col_type') }}</th>
                         <th class="px-4 py-3 text-right">{{ _('loyalty.store.terminal.col_points') }}</th>
+                        <th class="px-4 py-3">{{ _('loyalty.store.terminal.select_category') }}</th>
                         <th class="px-4 py-3">{{ _('loyalty.store.terminal.col_notes') }}</th>
                     </tr>
                 </thead>
                 <tbody class="bg-white divide-y dark:divide-gray-700 dark:bg-gray-800">
                     <template x-if="recentTransactions.length === 0">
                         <tr>
-                            <td colspan="5" class="px-4 py-6 text-center text-gray-500 dark:text-gray-400">
+                            <td colspan="6" class="px-4 py-6 text-center text-gray-500 dark:text-gray-400">
                                 {{ _('loyalty.store.terminal.no_recent_transactions') }}
                             </td>
                         </tr>
@@ -309,6 +310,7 @@
                             <td class="px-4 py-3 text-sm text-right font-medium"
                                 :class="tx.points_delta > 0 ? 'text-green-600' : 'text-orange-600'"
                                 x-text="(tx.points_delta > 0 ? '+' : '') + formatNumber(tx.points_delta)"></td>
+                            <td class="px-4 py-3 text-sm text-gray-500" x-text="tx.category_names?.join(', ') || '-'"></td>
                             <td class="px-4 py-3 text-sm text-gray-500" x-text="tx.notes || '-'"></td>
                         </tr>
                     </template>
@@ -331,9 +333,9 @@
         <div class="flex flex-wrap gap-2">
             <template x-for="cat in categories" :key="cat.id">
                 <button type="button"
-                        @click="selectedCategory = (selectedCategory === cat.id) ? null : cat.id"
+                        @click="selectedCategories.includes(cat.id) ? selectedCategories = selectedCategories.filter(id => id !== cat.id) : selectedCategories.push(cat.id)"
                         class="px-3 py-1.5 text-sm font-medium rounded-full border transition-colors"
-                        :class="selectedCategory === cat.id
+                        :class="selectedCategories.includes(cat.id)
                             ? 'bg-purple-600 text-white border-purple-600'
                             : 'bg-white text-gray-700 border-gray-300 hover:bg-gray-50 dark:bg-gray-700 dark:text-gray-300 dark:border-gray-600'"
                         x-text="cat.name">