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.

.agents/skills/tttk-authoring/reference.md

@@ -54,7 +54,6 @@ Nest with more colons (`::::`, `:::::`).
 | `:md-border` | color or border image | `width`, `slice` |
 | `:md-font` | font family | `source`, `weight`, `color` |
 | `:md-pins` | image path | `pins`, `fixed`, `labelStart` |
-| `:md-commander` | command template CSV | `placeholder`, `class`, `height` |
 | `:md-yarn-spinner` | Yarn Spinner file | `start` |
 
 ### `:md-dice`
@@ -205,19 +204,6 @@ Numbered markers on an image.
 :md-pins[./images/dungeon.png]{labelStart="1"}
 ```
 
-### `:md-commander`
-
-Interactive command history / tracker panel.
-
-The body is a CSV of command templates (`command,parameter,label,description,insertedText`).
-
-- Body: command template CSV
-- Attributes: `placeholder`, `class`, `height`
-
-```markdown
-:md-commander[./commands.csv]{placeholder="输入命令…" height="400px"}
-```
-
 ### `:md-yarn-spinner`
 
 Runs a Yarn Spinner dialogue file.