feat(loyalty): transaction categories (what was sold)

Merchants can configure per-store product categories (e.g., Men,
Women, Accessories, Kids) that sellers select when entering loyalty
transactions. Enables per-category sales analytics.

Backend:
- New model: StoreTransactionCategory (store-scoped, max 10 per store)
- Migration loyalty_007: creates table + adds category_id FK on
  loyalty_transactions
- New category_service.py with CRUD + validation
- New schemas/category.py (Create, Update, Response, ListResponse)
- Admin CRUD: GET/POST/PATCH/DELETE /admin/loyalty/stores/{id}/categories
- Store CRUD: GET/POST/PATCH/DELETE /store/loyalty/categories
- Stamp/Points request schemas accept optional category_id
- Stamp/Points services pass category_id to transaction creation
- TransactionResponse includes category_id + category_name

342 tests pass.

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

app/modules/loyalty/migrations/versions/loyalty_007_add_transaction_categories.py

@@ -0,0 +1,68 @@
+"""loyalty 007 - add transaction categories
+
+Adds store-scoped product categories (e.g., Men, Women, Accessories)
+that sellers select when entering loyalty transactions. Also adds
+category_id FK on loyalty_transactions.
+
+Revision ID: loyalty_007
+Revises: loyalty_006
+Create Date: 2026-04-19
+"""
+import sqlalchemy as sa
+
+from alembic import op
+
+revision = "loyalty_007"
+down_revision = "loyalty_006"
+branch_labels = None
+depends_on = None
+
+
+def upgrade() -> None:
+    op.create_table(
+        "store_transaction_categories",
+        sa.Column("id", sa.Integer(), primary_key=True, index=True),
+        sa.Column(
+            "store_id",
+            sa.Integer(),
+            sa.ForeignKey("stores.id"),
+            nullable=False,
+        ),
+        sa.Column("name", sa.String(100), nullable=False),
+        sa.Column("display_order", sa.Integer(), nullable=False, server_default="0"),
+        sa.Column("is_active", sa.Boolean(), nullable=False, server_default="true"),
+        sa.Column(
+            "created_at",
+            sa.DateTime(timezone=True),
+            server_default=sa.text("now()"),
+            nullable=False,
+        ),
+        sa.Column(
+            "updated_at",
+            sa.DateTime(timezone=True),
+            server_default=sa.text("now()"),
+            nullable=False,
+        ),
+        sa.UniqueConstraint("store_id", "name", name="uq_store_category_name"),
+    )
+    op.create_index(
+        "idx_store_category_store",
+        "store_transaction_categories",
+        ["store_id", "is_active"],
+    )
+
+    op.add_column(
+        "loyalty_transactions",
+        sa.Column(
+            "category_id",
+            sa.Integer(),
+            sa.ForeignKey("store_transaction_categories.id", ondelete="SET NULL"),
+            nullable=True,
+        ),
+    )
+
+
+def downgrade() -> None:
+    op.drop_column("loyalty_transactions", "category_id")
+    op.drop_index("idx_store_category_store", table_name="store_transaction_categories")
+    op.drop_table("store_transaction_categories")