(feature) Add managed rsync verbosity for dry-runs

Add default dry-run rsync output flags so long-running dry-runs expose
file-list, progress, stats, and itemized change information in their
run-specific log files.

Avoid duplicating user-supplied itemize or --info arguments so operators
can still tune rsync output from global or host configuration.

src/pobsync_backend/tests/test_run_scheduled_config_source.py

@@ -93,6 +93,8 @@ class RunScheduledConfigSourceTests(SimpleTestCase):
         def fake_run_rsync(command, log_path, timeout_seconds, cancel_check=None):
             self.assertEqual(log_path, Path("/tmp/pobsync-dryrun/web-01/run-42/rsync.log"))
             self.assertEqual(timeout_seconds, 900)
+            self.assertIn("--itemize-changes", command)
+            self.assertIn("--info=flist2,progress2,stats2", command)
             log_path.parent.mkdir(parents=True, exist_ok=True)
             log_path.write_text("run 42\n", encoding="utf-8")
             return RsyncResult(exit_code=0, command=command)
@@ -110,6 +112,30 @@ class RunScheduledConfigSourceTests(SimpleTestCase):
         self.assertEqual(result["log"], "/tmp/pobsync-dryrun/web-01/run-42/rsync.log")
         self.assertEqual(result["timeout_seconds"], 900)
 
+    def test_dry_run_does_not_duplicate_custom_output_args(self) -> None:
+        config_source = FakeConfigSource()
+
+        def effective_config_for_host(host: str) -> dict:
+            config = FakeConfigSource.effective_config_for_host(config_source, host)
+            config["rsync"]["args_effective"] = ["--archive", "--itemize-changes", "--info=name1,stats2"]
+            return config
+
+        config_source.effective_config_for_host = effective_config_for_host
+
+        with patch("pobsync.commands.run_scheduled.run_rsync") as run_rsync:
+            run_rsync.return_value = RsyncResult(exit_code=0, command=["rsync"])
+            run_scheduled(
+                prefix=Path("/missing-prefix"),
+                host="web-01",
+                dry_run=True,
+                config_source=config_source,
+            )
+
+        command = run_rsync.call_args.args[0]
+        self.assertEqual(command.count("--itemize-changes"), 1)
+        self.assertNotIn("--info=flist2,progress2,stats2", command)
+        self.assertIn("--info=name1,stats2", command)
+
     def test_dry_run_reports_cancelled_rsync(self) -> None:
         def fake_run_rsync(command, log_path, timeout_seconds, cancel_check=None):
             self.assertTrue(cancel_check())