Delete both folders and documents in a single atomic operation.

**Features:**
- Delete multiple folders and documents simultaneously
- Mixed selection support (folders + documents in one request)
- Automatic cascade deletion for folder contents
- Atomic operation with rollback on critical failures
- Comprehensive error reporting per item

**Request:**
- `folder_ids`: List of folder UUIDs to delete (optional)
- `document_ids`: List of document UUIDs to delete (optional)
- `reason`: Reason for deletion (required for audit trail)
- `cascade_delete`: If true, deletes all folder contents recursively (applies to folders only)

**Response:**
- `success_count`: Number of successfully deleted items (folders + documents)
- `failure_count`: Number of items that failed to delete
- `total_count`: Total number of items in the request
- `errors`: List of error details for failed deletions with item_id, item_type (folder/document), and error message
- `details`: Breakdown of folders vs documents deleted/failed

**Use Cases:**
- Delete selected items from folder contents view
- Clean up multiple items across different locations
- Batch delete operations from search results

**Notes:**
- At least one of `folder_ids` or `document_ids` must be provided
- Folders are processed before documents
- Non-empty folders will fail unless `cascade_delete=true`
- All deletions are soft deletes (can be recovered)
- Partial success is possible (some items deleted, others failed)

{
  "details": {
    "documents_deleted": 13,
    "documents_failed": 1,
    "folders_deleted": 5,
    "folders_failed": 2
  },
  "errors": [
    {
      "entity_id": "123e4567-e89b-12d3-a456-426614174000",
      "entity_name": "Tax Documents 2024",
      "entity_type": "folder",
      "error": "Folder is not empty. Use cascade_delete=true to delete contents."
    },
    {
      "entity_id": "987fcdeb-51a2-43f7-b890-123456789abc",
      "entity_name": "W2_Form.pdf",
      "entity_type": "document",
      "error": "Document is locked and cannot be deleted."
    }
  ],
  "failure_count": 3,
  "success_count": 18,
  "total_count": 21
}