The version tag previously existed only in git and the Docker image tag —
the running app had no way to report what build it was. Version is now
injected at build time via -ldflags into internal/version.Version (defaults
to "dev" for local builds), passed by the release workflow as the
APP_VERSION Docker build arg from the pushed tag.
Surfaced in Admin → Settings → About (extensible card for future rows like
disk space) and in the /health JSON response, so deployments can be
verified with curl alone.
