Add deterministic MDX linter to improve docs quality and consistency

[yasnazariel]

Overview

This PR introduces a custom MDX linter to enforce consistency and catch common documentation issues before merge.

What’s included

• Frontmatter validation (title, description)
• Code block language enforcement
• Internal link validation
• Basic structure checks (headings, components)

Improvements

• Lints only changed files by default using git diff
• Adds file system caching for faster link validation
• Reduces false positives in code block detection
• Provides clear error/warning output with line references

Why this matters

This helps prevent:

• Broken internal links
• Missing metadata
• Invalid MDX syntax
• Inconsistent documentation structure

Overall, it improves documentation reliability and reduces review overhead.

Usage

node scripts/lint-mdx.js        # changed files
node scripts/lint-mdx.js all    # all docs