feature: remove files with the draft extension prefix

The aim of this feature is to allow both a draft version and a "published" version to co-exist, a common use case in existing websites.
A file `my-post.md` could then co-exist with `my-post.draft.md`. The file is always removed, but when drafts are enabled the pointer to `my-post.md` is replaced with the file at `my-post.draft.md`

No files, tests, or entry points are named. Start by locating the plugin's draft detection and file-removal logic, then trace how the file pointer is selected when drafts are enabled. Done means my-post.md and my-post.draft.md can coexist, with the draft file replacing the pointer only when drafts are enabled.

Written by the indexing model from the issue text.