refactor(components): remove md-commander widget

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.

src/cli/validate/known.ts

@@ -131,16 +131,6 @@ export const KNOWN_ELEMENTS: readonly ElementSpec[] = [
       ':md-pins[./images/dungeon.png]{labelStart="1"}',
     ],
   },
-  {
-    name: "md-commander",
-    body: "command template CSV",
-    attrs: ["placeholder", "class", "height"],
-    summary: "Interactive command history / tracker panel.",
-    details:
-      "The body is a CSV of command templates (`command,parameter,label,description,insertedText`).",
-    refKind: "csv",
-    examples: [':md-commander[./commands.csv]{placeholder="输入命令…" height="400px"}'],
-  },
   {
     name: "md-yarn-spinner",
     body: "Yarn Spinner file",