(refactor) Use operator-facing config errors

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.

src/pobsync_backend/config_repository.py

@@ -85,7 +85,7 @@ def global_config_data(name: str = "default") -> dict[str, Any]:
     try:
         global_config = GlobalConfig.objects.get(name=name)
     except ObjectDoesNotExist as exc:
-        raise ConfigRepositoryError(f"Missing GlobalConfig {name!r}") from exc
+        raise ConfigRepositoryError(f"Missing global config {name!r}") from exc
     return _global_runtime_data(global_config)
 
 
@@ -93,5 +93,5 @@ def host_config_data(host: str) -> dict[str, Any]:
     try:
         host_config = HostConfig.objects.get(host=host, enabled=True)
     except ObjectDoesNotExist as exc:
-        raise ConfigRepositoryError(f"Missing enabled HostConfig {host!r}") from exc
+        raise ConfigRepositoryError(f"Missing enabled host {host!r}") from exc
     return _host_runtime_data(host_config)

src/pobsync_backend/retention.py

@@ -135,7 +135,7 @@ def _enabled_host_config(host: str) -> HostConfig:
     try:
         return HostConfig.objects.get(host=host, enabled=True)
     except HostConfig.DoesNotExist as exc:
-        raise ConfigError(f"Missing enabled HostConfig {host!r}") from exc
+        raise ConfigError(f"Missing enabled host {host!r}") from exc
 
 
 def _retention_for_host(host_config: HostConfig) -> dict[str, int]:

src/pobsync_backend/tests/test_config_repository.py

@@ -2,7 +2,7 @@ from __future__ import annotations
 
 from django.test import TestCase
 
-from pobsync_backend.config_repository import global_config_data, host_config_data
+from pobsync_backend.config_repository import ConfigRepositoryError, global_config_data, host_config_data
 from pobsync_backend.models import GlobalConfig, HostConfig
 
 
@@ -52,3 +52,12 @@ class ConfigRepositoryTests(TestCase):
         self.assertEqual(host_cfg["excludes_add"], ["/tmp/***"])
         self.assertNotIn("unknown", global_cfg)
         self.assertNotIn("unknown", host_cfg)
+
+    def test_missing_config_errors_use_operator_labels(self) -> None:
+        with self.assertRaisesMessage(ConfigRepositoryError, "Missing global config 'default'"):
+            global_config_data()
+
+        GlobalConfig.objects.create(name="default", backup_root="/backups")
+
+        with self.assertRaisesMessage(ConfigRepositoryError, "Missing enabled host 'web-01'"):
+            host_config_data("web-01")