Fix: Add _open() and path() methods to TenantAwareFileSystemStorage

Critical fix for Celery photo processing. The storage class now correctly
handles file reading operations by automatically adding tenant_id prefix
when opening files.

Problems fixed:
- Celery tasks could not open image files from storage
- PIL/Pillow couldn't locate files in tenant-specific directories
- temp file deletion was failing due to path validation

Changes:
- Added _open() method to add tenant_id prefix when opening files
- Added path() method to convert relative paths to full filesystem paths
- Updated delete() method to handle paths with or without tenant prefix
- All methods include security checks to prevent cross-tenant access

Testing:
- All 5 existing tests pass
- Verified photo processing task works end-to-end:
  * Reads temp image file from disk
  * Processes and creates all image versions
  * Saves processed files to tenant-specific directory
  * Cleans up temporary files correctly
- Files correctly stored in: media/tenants/{tenant_id}/products/{product_id}/{photo_id}/

🤖 Generated with Claude Code

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

myproject/pos/static/pos/js/terminal.js

@@ -98,7 +98,8 @@ function updateCustomerDisplay() {
   }
 
   // Обновляем видимость кнопок сброса (в корзине и в модалке продажи)
-  const isSystemCustomer = selectedCustomer.id === SYSTEM_CUSTOMER.id;
+  // Приводим к числу для надёжного сравнения (JSON может вернуть разные типы)
+  const isSystemCustomer = Number(selectedCustomer.id) === Number(SYSTEM_CUSTOMER.id);
 
   [document.getElementById('resetCustomerBtn'),
    document.getElementById('checkoutResetCustomerBtn')].forEach(resetBtn => {