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/inventory/migrations/0005_reservation_product_kit_and_more.py

@@ -0,0 +1,25 @@
+# Generated by Django 5.0.10 on 2025-11-20 12:09
+
+import django.db.models.deletion
+from django.db import migrations, models
+
+
+class Migration(migrations.Migration):
+
+    dependencies = [
+        ('inventory', '0004_showcase_is_default_and_more'),
+        ('orders', '0003_historicalorderitem_is_from_showcase_and_more'),
+        ('products', '0008_productkit_showcase_and_more'),
+    ]
+
+    operations = [
+        migrations.AddField(
+            model_name='reservation',
+            name='product_kit',
+            field=models.ForeignKey(blank=True, help_text='Временный комплект, для которого создан резерв', null=True, on_delete=django.db.models.deletion.CASCADE, related_name='reservations', to='products.productkit', verbose_name='Комплект'),
+        ),
+        migrations.AddIndex(
+            model_name='reservation',
+            index=models.Index(fields=['product_kit'], name='inventory_r_product_70aed5_idx'),
+        ),
+    ]