Add a `releases` command for deployment history (à la `heroku releases`)

Description of feature

Right now there's no way to list an app's past deployments from dokku itself. dokku ps:report and dokku git:report only show the current release (running container, current git SHA) — there's no record of what was deployed before that, when, or why a given deploy happened (git push vs. ps:rebuild vs. git:from-image, etc.).

In practice the only trail is the app's bare git repo (git log on the dokku host), which only covers git-triggered deploys, doesn't record build outcome/timestamp/trigger, and is easy to lose track of on hosts with many apps.

Heroku's heroku releases is the reference UX: a numbered list of releases per app, each with a version, description (e.g. "Deploy abc1234"), user, and timestamp, plus heroku releases:info for detail and heroku rollback to go back to one.

Proposed: a dokku releases:report <app> (or dokku releases <app>) command backed by a small persisted log (e.g. RELEASES file or sqlite under $DOKKU_ROOT/<app>/) that records one entry per successful release: sequence number, git SHA (if any), image tag/digest, trigger (git push / rebuild / from-image / cli), and timestamp. This would pair naturally with #7544 ("Retain old images on deploy") — once old images are kept around via keep-count, this gives users a way to actually see and pick which past release to roll back to, rather than only being told how many are kept.