Add _validate_cfg_values() to knoe/ui/screens/cfg.py — called before
_filter_cfg_values_for_persistence so MagicMock (or any non-str) widget
values raise TypeError instead of being silently str()-coerced into
conf/<mode>.cfg.
Also re-raise TypeError/ValueError from _save_knoe_cfg so the error
escapes the outer broad except-Exception handler.
New test: tests/installer/test_cfg_save_refuses_mock_values.py
- test_save_knoe_cfg_refuses_non_string_widget_values: MagicMock vars → TypeError
- test_save_knoe_cfg_real_strings_produce_clean_cfg: real _Var stubs → clean cfg
Fixes TODO-1 / tracked in docs/completed/todo-1-cfg-save-path-bug.md.
conf/k3d.cfg and conf/k3s.cfg still contain stale MagicMock values from
before this fix and must be regenerated before committing.
Co-authored-by: Junie <junie@jetbrains.com>
