fix(issue-45): restore stays off when python3 has no tomllib

The shim runs a bare python3. Before 3.11 the module failed to import and the
server started with restore on; now it gets the key alone, with a warning.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

tests/test_issue45_herdr_config.py

@@ -71,6 +71,14 @@ def test_a_bad_value_type_falls_back_to_minimal():
     assert warnings == []
 
 
+def test_without_tomllib_restore_is_still_off(monkeypatch):
+    # The shim runs a bare `python3`; on one older than 3.11 an import error
+    # would leave the server with restore on. Off wins over the user's settings.
+    monkeypatch.setattr(hc, "tomllib", None)
+    text, warnings = hc.server_config_text("[ui]\nconfirm_close = false\n")
+    assert text == hc.MINIMAL and "no tomllib" in warnings[0]
+
+
 def _env(tmp_path, **kw):
     env = {"HOME": str(tmp_path / "home")}
     env.update(kw)