gitignore command: local/global tsbuildinfo support

What's new

Adds verify-loop gitignore [local|global] to control where *.tsbuildinfo gets ignored.

Problem

TSC's incremental build cache (.tsbuildinfo) needs to be in .gitignore, but:

• Teammates may not know what the file is and remove it
• Adding it per-repo is repetitive across multiple projects

Commands

verify-loop gitignore global   # → writes to ~/.gitignore_global (or core.excludesFile)
                               #   removes *.tsbuildinfo from local .gitignore
                               #   saves preference to ~/.config/verify-loop/config.yml

verify-loop gitignore local    # → back to per-repo .gitignore (default)

The global path respects git config --global core.excludesFile if already configured, otherwise falls back to ~/.gitignore_global (works on Windows, Linux, macOS).

Preference is saved globally and applied on every subsequent TSC run — no per-project config needed.