feat: per-page SumUp models and migration (Phase 3)

- Migration: add market_place_id to cart_items, page_config_id to orders
- Order model: add page_config_id FK and page_config relationship
- CartItem model: add market_place_id FK and market_place relationship

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

alembic/versions/c3d4e5f6a7b8_add_page_tracking_to_orders.py

@@ -0,0 +1,55 @@
+"""add page_config_id to orders, market_place_id to cart_items
+
+Revision ID: c3d4e5f6a7b8
+Revises: b2c3d4e5f6a7
+Create Date: 2026-02-10
+"""
+from alembic import op
+import sqlalchemy as sa
+
+revision = 'c3d4e5f6a7b8'
+down_revision = 'b2c3d4e5f6a7'
+branch_labels = None
+depends_on = None
+
+
+def upgrade() -> None:
+    # 1. Add market_place_id to cart_items
+    op.add_column(
+        'cart_items',
+        sa.Column('market_place_id', sa.Integer(), nullable=True),
+    )
+    op.create_foreign_key(
+        'fk_cart_items_market_place_id',
+        'cart_items',
+        'market_places',
+        ['market_place_id'],
+        ['id'],
+        ondelete='SET NULL',
+    )
+    op.create_index('ix_cart_items_market_place_id', 'cart_items', ['market_place_id'])
+
+    # 2. Add page_config_id to orders
+    op.add_column(
+        'orders',
+        sa.Column('page_config_id', sa.Integer(), nullable=True),
+    )
+    op.create_foreign_key(
+        'fk_orders_page_config_id',
+        'orders',
+        'page_configs',
+        ['page_config_id'],
+        ['id'],
+        ondelete='SET NULL',
+    )
+    op.create_index('ix_orders_page_config_id', 'orders', ['page_config_id'])
+
+
+def downgrade() -> None:
+    op.drop_index('ix_orders_page_config_id', table_name='orders')
+    op.drop_constraint('fk_orders_page_config_id', 'orders', type_='foreignkey')
+    op.drop_column('orders', 'page_config_id')
+
+    op.drop_index('ix_cart_items_market_place_id', table_name='cart_items')
+    op.drop_constraint('fk_cart_items_market_place_id', 'cart_items', type_='foreignkey')
+    op.drop_column('cart_items', 'market_place_id')