Fix product reservation system for demo orders

PROBLEM ANALYSIS:
- SQL script created orders bypassing Django ORM
- Django signals (post_save) didn't trigger
- No reservations were created automatically
- Found 51 orders with 102 items and 0 reservations

SOLUTION IMPLEMENTED:

1. Updated create_demo_orders command:
   - Added clear documentation about ORM usage
   - Already uses ORM (.save()) which triggers signals
   - Added informative messages about automatic reservations

2. Created fix_missing_reservations command:
   - Finds OrderItems without reservations
   - Creates missing Reservation records
   - Supports --dry-run mode for safety
   - Handles missing warehouses gracefully

3. Created SQL fix script:
   - Direct SQL approach for existing data
   - Creates reservations for all 102 items
   - Status: 'reserved'
   - Verified: All items now have reservations

4. Added verification scripts:
   - check_orders.py: Shows orders/items/reservations count
   - run_fix_reservations.py: Executes SQL fix

RESULTS:
- ✓ 102 reservations created for existing orders
- ✓ Future orders will use ORM and create reservations automatically
- ✓ System now works correctly

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

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

myproject/run_fix_reservations.py

@@ -0,0 +1,32 @@
+"""
+Скрипт для создания резервов для существующих заказов
+"""
+import os
+import django
+
+os.environ.setdefault('DJANGO_SETTINGS_MODULE', 'myproject.settings')
+django.setup()
+
+from django.db import connection
+
+# Читаем SQL скрипт
+with open('fix_reservations.sql', 'r', encoding='utf-8') as f:
+    sql = f.read()
+
+# Выполняем SQL
+with connection.cursor() as cursor:
+    try:
+        cursor.execute(sql)
+        print("[OK] SQL script executed successfully!")
+        print("\nResults:")
+        # Получаем результат последнего SELECT
+        rows = cursor.fetchall()
+        if rows:
+            row = rows[0]
+            print(f"  Total items: {row[0]}")
+            print(f"  Items with reservations: {row[1]}")
+            print(f"  Items without reservations: {row[2]}")
+        print("\n[OK] Reservations created!")
+    except Exception as e:
+        print(f"[ERROR] {e}")
+        raise