Clear the reused dry-run rsync log before each dry-run so run details
only show output from the current execution.
Populate new Django global configs with the existing safe rsync and
exclude defaults, including archive mode and standard pseudo-filesystem
exclusions.
Add a host check that fails when effective rsync args do not include
archive or recursive transfer, preventing real backups that only report
"skipping directory .".
Include the selected SSH credential metadata and rsync log tail in
dry-run and failed backup results so Django shows the actual SSH or
rsync failure instead of only the exit code.
Warn in host checks when a host still uses database-stored private key
material, making it easier to spot old credentials after switching to
generated filesystem keys.
Introduce a ConfigSource interface so scheduled backups no longer need
to load host configuration directly from runtime YAML. Add a Django-backed
config source for SQL-driven backup runs, keep file-based config as the
CLI default, and make scheduled prune execution actually apply retention
after successful runs.
