`Changes` page lists files not tracked by git

It would be useful to filter out untracked files from the `Changes` page. For example, all the `docs/superpowers/` files here are not tracked in git.

Start at the Changes page and trace how it determines which files to display, using the untracked docs/superpowers/ files as the example case. Done means files not tracked by git no longer appear on the Changes page while tracked changes remain visible.

索引モデルが issue の本文から書いたものです。