(refactor) Normalize maintainer command labels

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.

src/pobsync_backend/management/commands/configure_pobsync_host.py

@@ -10,7 +10,7 @@ from pobsync_backend.models import GlobalConfig, HostConfig
 
 
 class Command(BaseCommand):
-    help = "Create or update a SQL-backed host pobsync configuration."
+    help = "Create or update a host backup configuration."
 
     def add_arguments(self, parser) -> None:
         parser.add_argument("host")
@@ -29,7 +29,7 @@ class Command(BaseCommand):
     def handle(self, *args: Any, **options: Any) -> None:
         host = sanitize_host(options["host"])
         if HostConfig.objects.filter(host=host).exists() and not options["force"]:
-            raise CommandError(f"HostConfig {host!r} already exists; use --force to update")
+            raise CommandError(f"Host {host!r} already exists; use --force to update")
 
         retention = self._retention(options["retention"])
         defaults = {
@@ -49,7 +49,7 @@ class Command(BaseCommand):
         }
         _obj, created = HostConfig.objects.update_or_create(host=host, defaults=defaults)
         action = "Created" if created else "Updated"
-        self.stdout.write(self.style.SUCCESS(f"{action} HostConfig {host!r}."))
+        self.stdout.write(self.style.SUCCESS(f"{action} host {host!r}."))
 
     def _retention(self, value: str | None) -> dict[str, int]:
         if value: