feat(analysis): add --commit option for historical codebase analysis

Add a --commit CLI option to directory-based analysers (UnifiedParser,
RawTextParser, GitLogParser RepoScanCommand) that creates a temporary
git worktree at the specified commit and runs analysis against it.

Supports commit hashes, tags, branches, relative refs (HEAD~5), and
date expressions ("2 years ago", "2024-01-15"). Output files are
automatically prefixed with the short commit hash.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>