The journal now owns command history and tracking, so retire the md-commander widget. Its dice engine was extracted to src/components/dice in the previous commit.
Removes the custom element, tracker/command stores, completions, useCommander, Emmet parser, the doc entry, test fixtures, and the known-element catalog entry (reference docs regenerated).
BREAKING CHANGE: :md-commander is no longer a known element; content using it now fails tttk check with TTTK-D001.