Markdown Link Formatter

When the user asks to convert their markdown to use reference-style links:

1. Read the target file.
2. Collect every inline [text](url) occurrence.
3. Rewrite the body to [text][n] and append a reference block at the bottom.
4. Preserve ordering of first appearance.

Notes:

• Do not modify code fences or HTML blocks.
• Leave already-referenced links alone.