v1.27.4

Hotfix: restore the bragi-tasks sidecar's migration step after the
PyPI-image cutover. v1.27.1's minimal Dockerfile shape dropped the
project-root alembic.ini from the image, so scheduler.sh's bare
alembic upgrade head invocation failed with No 'script_location' key found in configuration on every container start. The sidecar
crashlooped, scheduled tasks (publish, embeds, webmentions,
ActivityPub, renditions, db analyze, vacuum) never ran. Admin and
delivery web containers still came up because the /data/.migrated
sentinel from the prior deploy persisted on the volume.

Fixed

• docker/scheduler.sh now invokes bragi db upgrade instead of
  bare alembic upgrade head. The bragi db upgrade CLI command
  (added in v1.27.0) wraps alembic against the wheel-bundled
  bragi:alembic scripts and works from any cwd without an
  alembic.ini on disk -- the canonical migration entry-point for
  the PyPI-installed image shape. The bare alembic CLI continues to
  work in dev against the project-root alembic.ini.