Retire the old YAML and cron oriented pobsync CLI commands and expose a
SQL-first Django-backed command surface instead. Add schedule and
retention management commands, move shared defaults/parsing out of legacy
commands, remove obsolete command modules, and update documentation and
tests for the new workflow.
Build runtime pobsync configuration exclusively from structured SQL
fields, leaving legacy JSON only for import and audit context. Add
SQL-first management commands for global and host configuration and
cover them with tests.
