[guillaume-d]

Adds an opt-in Vale pre-commit hook that checks spelling and style in staged text, markup, and source files using the configurable line-aware command hooks merged in #757.

Implements the requirements described in this PR and its prerequisites:

• Enable Vale with PreCommit: { Vale: { enabled: true } }; no Ruby plugin is needed. The default command is vale --output=line, with executable detection, installation guidance, and configurable file selection.
• Parse file and line locations, including Windows drive-letter paths and filenames containing spaces, and honor include, exclude, requires_files, and problem_on_unmodified_line.
• Preserve the stated severity limitation: diagnostics from unsuccessful commands default to errors because Vale's line output lacks severity. Documentation links to vale-cli/vale#350 for a custom template and explains the configuration needed to distinguish warnings.
• Replace the documentation placeholder with installation, setup, enablement, and customization instructions. Allow supported configuration regexes through YamlSyntax, while continuing to reject arbitrary Ruby objects.

Validation: all 1,866 local examples pass, including 20 Vale-specific examples, a real subprocess with staged files, and YAML regression coverage. All repository pre-commit checks and RuboCop pass. A smoke test using the checksum-verified Vale 3.26.0 release confirms both failing diagnostics and a clean-file pass with a staged filename containing spaces. GitHub CI tests Ruby 3.3, 3.4, and 4.0 on Ubuntu and Windows.

[guillaume-d]

This depends on #757 which should be merged first! I will rebase this (or merge from master?) after that.

Rebased to adapt to latest configuration format changes.