docs(tools): add Vale prose linter section

[gwtaylor]

Adds a new section about Vale, a syntax-aware prose linter for documentation and markdown files.

The new section:

• Explains what Vale is and its benefits for maintaining documentation consistency
• Provides installation instructions for macOS
• Shows basic usage examples for linting files and directories
• Mentions configuration via .vale.ini
• Highlights pre-commit integration and GitHub Workflow options
• Follows the same style as existing Jupytext, Ruff, and Markdownlint sections
• Positioned in the "Formatting and Linting" section after Markdownlint for thematic consistency