fix: resolve Git paths in linked worktrees

Problem

Gitlint and its hook installer assume .git is a directory. In a standard linked Git worktree, .git is a pointer file. A configured hook such as gitlint --edit .git/COMMIT_EDITMSG therefore resolves to an invalid path and blocks otherwise valid commits with ENOTDIR.

The hook installer also joins <worktree>/.git/hooks, which cannot locate the repository's effective hooks directory in a linked worktree.

Acceptance criteria

• --edit .git/COMMIT_EDITMSG resolves through git rev-parse --git-path when .git is a pointer file.
• Ordinary absolute and relative commit-message paths remain unchanged.
• Hook installation and removal use Git's resolved hooks directory.
• Tests exercise a real linked worktree rather than mocking the path layout.
• A patch release is published and downstream Stacks consumes it.