Reuses RepoScanner.IsRepo (now public) to validate WorkingDir whenever it
changes in ListSettingsModalViewModel — Browse or typing. A missing folder
or a non-repo folder shows an inline warning and gates Save via the same
CanExecute pattern the load-failure gate already uses; an empty WorkingDir
is untouched. Previously this only surfaced as a Failed task deep in
WorktreeManager on first run.
Also localizes the two hardcoded EN strings in the same file (delete
confirm, planning-sessions block) into vm.listSettings.* keys.
mika kuns
3348736e9d