Title: Add case-folding support for Markdown parsing

[Dubb3d4nny]

Description: This PR introduces case-folding support in the Markdown parser to handle case-insensitive matching for headings, links, and anchors. The update modifies markdown.js to ensure consistent anchor generation regardless of text casing, improving compatibility with various Markdown sources.

Testing:

• Verified that headings with mixed case now produce the same anchor IDs.
• Confirmed backward compatibility with existing Markdown behavior.

[Dubb3d4nny]

Hi Dear maintainer,

I've implemented the requested Markdown anchor update — it now handles case-insensitive matching for consistent behavior. Please review and merge at your earliest convenience, as this fix is time-sensitive.

Thanks for your quick attention!