refactor: inject config sources into scheduled backups

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.

src/pobsync_backend/tests/test_run_scheduled_config_source.py

@@ -0,0 +1,79 @@
+from __future__ import annotations
+
+from pathlib import Path
+from tempfile import TemporaryDirectory
+from unittest.mock import patch
+
+from django.test import SimpleTestCase
+
+from pobsync.commands.run_scheduled import run_scheduled
+from pobsync.rsync import RsyncResult
+
+
+class FakeConfigSource:
+    def __init__(self, backup_root: str = "/tmp/pobsync-test-backups") -> None:
+        self.backup_root = backup_root
+
+    def effective_config_for_host(self, host: str) -> dict:
+        return {
+            "backup_root": self.backup_root,
+            "host": host,
+            "address": "example.test",
+            "ssh": {"user": "root", "port": 22, "options": []},
+            "rsync": {
+                "binary": "rsync",
+                "args_effective": ["--archive"],
+                "timeout_seconds": 0,
+                "bwlimit_kbps": 0,
+            },
+            "source_root": "/",
+            "includes": [],
+            "excludes_effective": [],
+            "retention": {"daily": 7, "weekly": 4, "monthly": 3, "yearly": 1},
+        }
+
+
+class RunScheduledConfigSourceTests(SimpleTestCase):
+    def test_dry_run_uses_injected_config_source(self) -> None:
+        with patch("pobsync.commands.run_scheduled.run_rsync") as run_rsync:
+            run_rsync.return_value = RsyncResult(exit_code=0, command=["rsync", "--archive"])
+
+            result = run_scheduled(
+                prefix=Path("/missing-prefix"),
+                host="web-01",
+                dry_run=True,
+                config_source=FakeConfigSource(),
+            )
+
+        self.assertTrue(result["ok"])
+        self.assertEqual(result["host"], "web-01")
+        run_rsync.assert_called_once()
+
+    def test_successful_real_run_applies_prune_when_requested(self) -> None:
+        with TemporaryDirectory() as tmp:
+            prefix = Path(tmp) / "home"
+            with (
+                patch("pobsync.commands.run_scheduled.run_rsync") as run_rsync,
+                patch("pobsync.commands.retention_apply.run_retention_plan") as plan,
+            ):
+                run_rsync.return_value = RsyncResult(exit_code=0, command=["rsync", "--archive"])
+                plan.return_value = {
+                    "ok": True,
+                    "delete": [],
+                    "keep": [],
+                    "reasons": {},
+                    "protect_bases": False,
+                }
+
+                result = run_scheduled(
+                    prefix=prefix,
+                    host="web-01",
+                    dry_run=False,
+                    prune=True,
+                    prune_max_delete=10,
+                    config_source=FakeConfigSource(backup_root=str(Path(tmp) / "backups")),
+                )
+
+        self.assertTrue(result["ok"])
+        self.assertIsNotNone(result["prune"])
+        self.assertEqual(result["prune"]["deleted"], [])