Publishes a draft: flips draft: true off and re-dates the post to today.

Usage

mix cherry.publish content/posts/2026-08-14-my-draft.md [--source DIR] [--json]
mix cherry.publish my-draft [--source DIR] [--json]

The draft can be named by path or by slug — the same slug gen.post returns in its envelope. The file is renamed to today's date (the filename is the source of truth for a post's date) and the draft: line is removed. With --json, the envelope carries the old and new paths.