Fix Product filtering and add kit disassembly functionality

Fixed:
- Replace is_active with status='active' for Product filtering in IncomingModelForm
- Product model uses status field instead of is_active

Added:
- Showcase field to ProductKit for tracking showcase placement
- product_kit field to Reservation for tracking kit-specific reservations
- Disassemble button in POS terminal for showcase kits
- API endpoint for kit disassembly (release reservations, mark discontinued)
- Improved reservation filtering when dismantling specific kits

Changes:
- ShowcaseManager now links reservations to specific kit instances
- POS terminal modal shows disassemble button in edit mode
- Kit disassembly properly updates stock aggregates

🤖 Generated with [Claude Code](https://claude.com/claude-code)

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

myproject/pos/urls.py

@@ -23,6 +23,8 @@ urlpatterns = [
     path('api/product-kits/<int:kit_id>/', views.get_product_kit_details, name='get-product-kit-details'),
     # Обновить временный комплект (состав, фото, цены) [POST]
     path('api/product-kits/<int:kit_id>/update/', views.update_product_kit, name='update-product-kit'),
+    # Разобрать витринный комплект (освободить резервы, установить статус discontinued) [POST]
+    path('api/product-kits/<int:kit_id>/disassemble/', views.disassemble_product_kit, name='disassemble-product-kit'),
     # Создать временный комплект и зарезервировать на витрину [POST]
     path('api/create-temp-kit/', views.create_temp_kit_to_showcase, name='create-temp-kit-api'),
 ]