feat: replace color field with colors ManyToManyField in items model

- Updated `Item` model to use a ManyToManyField for colors, replacing the old ForeignKey relationship
- Modified templates to handle multiple color swatches in product details
- Updated admin for managing colors with `filter_horizontal`
- Adjusted views to prefetch related `colors` data for items
- Added migration to apply database changes

items/migrations/0005_remove_item_color_item_colors.py

@@ -0,0 +1,22 @@
+# Generated by Django 6.0.5 on 2026-05-25 22:17
+
+from django.db import migrations, models
+
+
+class Migration(migrations.Migration):
+
+    dependencies = [
+        ('items', '0004_color_item_discount_price_item_is_new_item_color'),
+    ]
+
+    operations = [
+        migrations.RemoveField(
+            model_name='item',
+            name='color',
+        ),
+        migrations.AddField(
+            model_name='item',
+            name='colors',
+            field=models.ManyToManyField(blank=True, related_name='items', to='items.color', verbose_name='Цвета'),
+        ),
+    ]