Replace remaining model-name based configuration errors with labels that
match the Django-first operating model.
Add coverage for missing global config and host configuration errors so
operator-facing messages stay readable.
Prefer --schedule-expression for scripted schedule updates while keeping
--cron as a compatibility alias.
Clean up management command help, errors, and output so operator-facing
text talks about hosts, global config, and Django backup configuration
instead of model names or old SQL-backed pobsync wording.
Drop the unused GlobalConfig.data field and remove the remaining YAML
config path helpers from PobsyncPaths.
Keep HostConfig.config as runtime state for preflight data, and relabel it
in the admin so it no longer reads as legacy compatibility storage.
Drop the obsolete pobsync_home field from GlobalConfig and remove it from
runtime config generation, form saves, and configuration commands.
The runtime state root now comes exclusively from POBSYNC_HOME/settings,
which keeps the Django model focused on backup behavior instead of install
layout.
Drop the pre-Django YAML import/export management commands and remove the
file-based config loader fallback from the backup and retention engines.
Keep the runtime config bridge backed by Django models, and add tests that
ensure engine operations require an explicit Django config source.
Hide the old pobsync_home field from the Django admin and replace legacy
operator-facing labels with runtime state root and backup root terminology.
Rename admin compatibility fieldsets, update self-check/config-check text,
and refresh management command help so Django/systemd stays the primary
mental model.
Remove the short pobsync aliases for global config, host config, and
schedule changes so the public CLI no longer points operators toward the
old configuration workflow.
Keep operational aliases for backup, discovery, retention, worker, and
scheduler debugging, and document explicit Django management commands for
automation use.
