feat: add Git diff preload toggle in Settings and respect it in diff loading#298

Dimillian merged 4 commits intomainDimillian/CodexMonitor:mainfrom

codex/github-mention-perf]-large-git-changes-freezes-the-appDimillian/CodexMonitor:codex/github-mention-perf]-large-git-changes-freezes-the-appCopy head branch name to clipboard