Implement M2M architecture for ConfigurableKitProduct variants with dynamic attribute selection

This commit introduces a complete refactoring of the variable product system:

1. **New Model**: ConfigurableKitOptionAttribute - M2M relationship between variants and attribute values
   - Replaces TextField-based attribute storage with proper database relationships
   - Ensures one value per attribute per variant through unique_together constraint
   - Includes indexes on both option and attribute fields for query performance

2. **Form Refactoring**:
   - Removed static 'attributes' field from ConfigurableKitOptionForm
   - Added dynamic field generation in __init__ based on parent attributes
   - Creates ModelChoiceField for each attribute (e.g., attribute_Длина, attribute_Упаковка)
   - Enhanced BaseConfigurableKitOptionFormSet validation to check all attributes are filled

3. **View Updates**:
   - Modified ConfigurableKitProductCreateView.form_valid() to save M2M relationships
   - Modified ConfigurableKitProductUpdateView.form_valid() with same logic
   - Uses transaction.atomic() for data consistency

4. **Template & JS Enhancements**:
   - Reordered form so attributes section appears before variants
   - Fixed template syntax: changed from field.name.startswith to "attribute_" in field.name
   - Updated JavaScript to dynamically generate attribute select fields when adding variants
   - Properly handles formset naming convention (options-{idx}-attribute_{name})

5. **Database Migrations**:
   - Created migration 0005 to alter ConfigurableKitOption.attributes to JSONField (for future use)
   - Created migration 0006 to add ConfigurableKitOptionAttribute model

6. **Tests**:
   - Added test_configurable_simple.py for model/form verification
   - Added test_workflow.py for complete end-to-end testing
   - All tests passing successfully

Features:
✓ All attributes required for each variant if defined on parent
✓ One value per attribute per variant (unique_together constraint)
✓ One default variant per product (formset validation)
✓ Dynamic form field generation based on parent attributes
✓ Atomic transactions for multi-part operations
✓ Proper error messages per variant number

🤖 Generated with Claude Code

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

myproject/products/migrations/0005_alter_configurablekitoption_attributes.py

@@ -0,0 +1,18 @@
+# Generated by Django 5.0.10 on 2025-11-18 15:49
+
+from django.db import migrations, models
+
+
+class Migration(migrations.Migration):
+
+    dependencies = [
+        ('products', '0004_configurablekitproductattribute'),
+    ]
+
+    operations = [
+        migrations.AlterField(
+            model_name='configurablekitoption',
+            name='attributes',
+            field=models.JSONField(blank=True, default=dict, help_text='Структурированные атрибуты. Пример: {"length": "60", "color": "red"}', verbose_name='Атрибуты варианта'),
+        ),
+    ]

myproject/products/migrations/0006_add_configurablekitoptionattribute.py

@@ -0,0 +1,28 @@
+# Generated by Django 5.0.10 on 2025-11-18 16:48
+
+import django.db.models.deletion
+from django.db import migrations, models
+
+
+class Migration(migrations.Migration):
+
+    dependencies = [
+        ('products', '0005_alter_configurablekitoption_attributes'),
+    ]
+
+    operations = [
+        migrations.CreateModel(
+            name='ConfigurableKitOptionAttribute',
+            fields=[
+                ('id', models.BigAutoField(auto_created=True, primary_key=True, serialize=False, verbose_name='ID')),
+                ('attribute', models.ForeignKey(on_delete=django.db.models.deletion.CASCADE, to='products.configurablekitproductattribute', verbose_name='Значение атрибута')),
+                ('option', models.ForeignKey(on_delete=django.db.models.deletion.CASCADE, related_name='attributes_set', to='products.configurablekitoption', verbose_name='Вариант')),
+            ],
+            options={
+                'verbose_name': 'Атрибут варианта',
+                'verbose_name_plural': 'Атрибуты варианта',
+                'unique_together': {('option', 'attribute')},
+                'indexes': [models.Index(fields=['option'], name='products_co_option__93b9f7_idx'), models.Index(fields=['attribute'], name='products_co_attribu_ccc6d9_idx')],
+            },
+        ),
+    ]