v0.3.0

Database and image updates

Apps and databases now run their image pinned by digest. Before, every
start pulled the tag again, so a restart or a crash could move a
database to a newer build, or an app on a moving tag to a new version,
with no backup first.

Once a day Zelie checks whether an image's tag points at a newer build.
The app page then shows it, with versions when the image gives them,
and Update deploys it. A database is backed up first; if the new build
does not start, the old one runs again.

A database can be upgraded to a new major version from its Settings
tab. Its data moves over as a dump onto a new volume; the old files are
kept on the Storage tab until you remove them.