markdown: Fix render list item blocks

[wabzqem]

Closes #[issue number]

Description

Markdown block elements such as fenced code blocks, tables, blockquotes, and headings were being dropped when nested inside list items. These blocks now render at the full available list width, with regression coverage for visibility and code-block action alignment.

Screenshot

Before	After

How to Test

Run cargo run --example markdown with this fix applied:

# Hello, **World**!
  
1. This is the first list item Hello!
    ```text
    a nested block
    ```
2. second list item
  
```text
non-nested block
```

Checklist

• [ X ] I have read the CONTRIBUTING document and followed the guidelines.
• [ X ] Reviewed the changes in this PR and confirmed AI generated code (If any) is accurate.
• [ X ] Passed cargo run for story tests related to the changes.