feat: make Django configs drive backups and scheduling

Treat SQL-backed Django models as the source of truth for pobsync
configuration, exporting runtime YAML only as a compatibility layer for
the existing engine. Add a database-driven scheduler command, Docker
scheduler services, schedule run-state fields, and tests for scheduler,
config export, and retention behavior.

src/pobsync_backend/management/commands/run_pobsync_backup.py

@@ -8,8 +8,8 @@ from django.core.management.base import BaseCommand, CommandError
 from django.utils import timezone
 
 from pobsync.commands.run_scheduled import run_scheduled
-from pobsync.config.load import load_host_config
 from pobsync.paths import PobsyncPaths
+from pobsync_backend.config_repository import export_runtime_configs
 from pobsync_backend.models import BackupRun, HostConfig
 
 
@@ -27,19 +27,12 @@ class Command(BaseCommand):
     def handle(self, *args: Any, **options: Any) -> None:
         host_name = options["host"]
         paths = PobsyncPaths(home=Path(options["prefix"]))
-        host_path = paths.hosts_dir / f"{host_name}.yaml"
-        if not host_path.exists():
-            raise CommandError(f"Missing host config: {host_path}")
+        try:
+            host = HostConfig.objects.get(host=host_name, enabled=True)
+        except HostConfig.DoesNotExist as exc:
+            raise CommandError(f"Missing enabled HostConfig {host_name!r}") from exc
 
-        host_cfg = load_host_config(host_path)
-        host, _created = HostConfig.objects.update_or_create(
-            host=host_cfg["host"],
-            defaults={
-                "address": host_cfg["address"],
-                "config": host_cfg,
-                "enabled": True,
-            },
-        )
+        export_runtime_configs(prefix=paths.home, host=host.host)
 
         run = BackupRun.objects.create(
             host=host,