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/migrations/versions/loyalty_008_add_category_translations.py

@@ -0,0 +1,33 @@
+"""loyalty 008 - add name_translations to transaction categories
+
+Adds a JSON column for multi-language category names alongside the
+existing name field (used as fallback/default).
+
+Revision ID: loyalty_008
+Revises: loyalty_007
+Create Date: 2026-04-19
+"""
+import sqlalchemy as sa
+
+from alembic import op
+
+revision = "loyalty_008"
+down_revision = "loyalty_007"
+branch_labels = None
+depends_on = None
+
+
+def upgrade() -> None:
+    op.add_column(
+        "store_transaction_categories",
+        sa.Column(
+            "name_translations",
+            sa.JSON(),
+            nullable=True,
+            comment='Language-keyed name dict, e.g. {"en": "Men", "fr": "Hommes"}',
+        ),
+    )
+
+
+def downgrade() -> None:
+    op.drop_column("store_transaction_categories", "name_translations")