Ensure list items have a list parent

### Context
List items must have a list parent. Adding a list item without a list parent is [deprecated](https://github.com/docling-project/docling-core/blob/20d74065e1c6c3a403b29a3ff5b76b86aa56e7f3/docling_core/types/doc/document.py#L2291-L2292) and will soon be forbidden.

### Task
Review all DoclingDocument creation code and ensure all added list items have a parent that is a list group (either unordered or ordered).

This includes all invocations of:
- `add_list_item()`, and
- `add_text()` were a list item may be passed

👉 see search here:
https://github.com/search?q=org%3Adocling-project+%28%22add_list_item%22+OR+%22add_text%22%29&type=code