chore: update lxml version

[mziv]

Summary

Updates lxml dependency to 6.0.

List of files changed and why

To upgrade the lxml constraint and regenerate the lock file, these files were touched: pyproject.toml uv.lock

How Has This Been Tested?

Tested parsing markdown of websites locally.

Checklist:

• [x] My code follows the style guidelines of this project
• [x] I have performed a self-review of my own code
• [ ] I have commented my code, particularly in hard-to-understand areas
• [ ] I have made corresponding changes to the documentation
• [ ] I have added/updated unit tests that prove my fix is effective or that my feature works
• [x] New and existing unit tests pass locally with my changes

Summary by CodeRabbit

• Chores
  • Updated dependency constraint to allow the newer lxml 6.x series, so installations may pull a newer lxml on next update.
  • Minor dependency list formatting tweak (no behavioral impact).
  • No changes to public APIs or user-facing functionality; app behavior remains the same.