Add is_default field to Showcase admin interface

- Add is_default to list_display and list_filter
- Include is_default in fieldsets for editing

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

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

myproject/inventory/admin.py

@@ -14,13 +14,13 @@ from inventory.models import (
 # ===== SHOWCASE =====
 @admin.register(Showcase)
 class ShowcaseAdmin(admin.ModelAdmin):
-    list_display = ('name', 'warehouse', 'is_active', 'created_at')
+    list_display = ('name', 'warehouse', 'is_default', 'is_active', 'created_at')
-    list_filter = ('is_active', 'warehouse', 'created_at')
+    list_filter = ('is_active', 'is_default', 'warehouse', 'created_at')
     search_fields = ('name', 'warehouse__name')
     date_hierarchy = 'created_at'
     fieldsets = (
         ('Основная информация', {
-            'fields': ('name', 'warehouse', 'description', 'is_active')
+            'fields': ('name', 'warehouse', 'description', 'is_active', 'is_default')
         }),
         ('Даты', {
             'fields': ('created_at', 'updated_at'),