LLM Markdown: Fix duplicate content in table cells

[reakaleek]

Closes #2316

Problem

When rendering markdown tables for LLM consumption, link labels and formatted text were duplicated.

Example of the bug:

| [Security configurations](https://...security)Security configurations | Full control |

Cause

The RenderTableCellContent method used cell.Descendants().OfType<Inline>() which returns all nested inline elements. This caused container inlines (links, bold, italic) and their child text to be rendered separately.

Solution

Changed to render the cell's child blocks directly using WriteChildren(cell). This properly handles the inline hierarchy without duplication.

Testing

Added 7 new tests covering:

• Links in tables and paragraphs
• Multiple links in same cell
• Bold and italic text in tables
• Images in tables
• Code inline in tables

All 35 LLM markdown tests pass.