The external editor flow (Ctrl+G, plan editor, /todo edit) warned 'No
editor configured' on Windows because getEditorCommand() returned
undefined whenever neither $VISUAL nor $EDITOR was set — the default
state for most Windows shells.
Fall back to 'notepad' on win32 after consulting $VISUAL/$EDITOR
(always present in %SystemRoot%\\System32) and trim env values so
accidentally padded strings still resolve. POSIX still returns
undefined so the warning continues to nudge users to configure an
editor.
Fixes#2604
metaphorics