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/products/models/kits.py

@@ -104,12 +104,23 @@ class ProductKit(BaseProductEntity):
         help_text="Заказ, для которого создан временный комплект"
     )
 
+    showcase = models.ForeignKey(
+        'inventory.Showcase',
+        on_delete=models.SET_NULL,
+        null=True,
+        blank=True,
+        related_name='temporary_kits',
+        verbose_name="Витрина",
+        help_text="Витрина, на которой выложен временный комплект"
+    )
+
     class Meta:
         verbose_name = "Комплект"
         verbose_name_plural = "Комплекты"
         indexes = [
             models.Index(fields=['is_temporary']),
             models.Index(fields=['order']),
+            models.Index(fields=['showcase']),
         ]
         constraints = [
             # Уникальное имя для активных комплектов (исключаем архивированные и снятые)