Create a footer that shows the last 5? recently modified entries.

This may be problematic because the `open` command delegates the editing to an external editor, and we can't track it. It may be possible to use a git command when publishing git a file list diff and use that to update the footer at publish time, but that can have it's own issues.

The issue mentions the open command, external editing, and publishing; start by tracing those command paths and how journal entries are updated. Determine whether a git file-list diff can identify recently modified entries, then verify that publishing produces a footer listing the five most recent entries.

Written by the indexing model from the issue text.