(bugfix) Guard dry-run logs and recursive rsync defaults

Clear the reused dry-run rsync log before each dry-run so run details
only show output from the current execution.

Populate new Django global configs with the existing safe rsync and
exclude defaults, including archive mode and standard pseudo-filesystem
exclusions.

Add a host check that fails when effective rsync args do not include
archive or recursive transfer, preventing real backups that only report
"skipping directory .".

src/pobsync_backend/host_ops.py

@@ -78,9 +78,31 @@ def collect_host_checks(host: HostConfig, global_config: GlobalConfig | None = N
     checks.append(_host_path_check("Host backup root", host_root, must_exist=True, must_be_writable=True))
     for subdir in HOST_BACKUP_SUBDIRS:
         checks.append(_host_path_check(f"Host directory: {subdir}", host_root / subdir, must_exist=True, must_be_writable=True))
+    checks.append(_rsync_recursion_check(host, global_config))
     return checks
 
 
+def _rsync_recursion_check(host: HostConfig, global_config: GlobalConfig) -> SelfCheck:
+    args = [*list(global_config.rsync_args or []), *list(global_config.rsync_extra_args or []), *list(host.rsync_extra_args or [])]
+    if _has_recursive_rsync_arg(args):
+        return SelfCheck("Host rsync recursion", "ok", "Rsync args include archive or recursive transfer.", " ".join(args))
+    return SelfCheck(
+        "Host rsync recursion",
+        "failed",
+        "Rsync args do not include archive or recursive transfer.",
+        "Add --archive or --recursive before running a real backup.",
+    )
+
+
+def _has_recursive_rsync_arg(args: list[str]) -> bool:
+    for arg in args:
+        if arg in {"--archive", "--recursive"}:
+            return True
+        if arg.startswith("-") and not arg.startswith("--") and any(flag in arg for flag in ("a", "r")):
+            return True
+    return False
+
+
 def _host_path_check(
     name: str,
     path: Path,