Init Reset Product V6

Initialize reset product flow V6 (NO CREDIT DEDUCTION HERE).

Steps:

1. Get product to reset (from request.product_id or user's active product)
2. Set product.is_active = False
3. Set user.is_resetting_product = True (for frontend redirect logic)
4. Set auto_schedule_settings.is_enabled = False
5. Clear scheduled queue entries for this product
6. Keep agent assignments active (will transfer to new product later)
7. Return old_product_id for agent transfer

NOTE: Credits are deducted during create-v6, not here. This allows users to abandon and retry without losing credits.