refactor: replace command link interception with :cmd[] directive

Replace the previous mechanism of intercepting specific command-prefixed
anchor tags with a dedicated `:cmd[]` markdown directive.

- Implement `cmdDirective` for `marked-directive` support.
- Update `CommandLinkManager` to listen for clicks on `[data-cmd]` spans
  instead of parsing `href` attributes.
- Add CSS styles for the new `.cmd-link` class.

src/markdown/index.ts

@@ -7,6 +7,7 @@ import { gfmHeadingId } from "marked-gfm-heading-id";
 import markedColumns from "./columns";
 import markedCodeBlockYamlTag from "./code-block-yaml-tag";
 import { iconDirective, setIconBase } from "./icon";
+import { cmdDirective } from "./cmd";
 
 // 使用 marked-directive 来支持指令语法
 const marked = new Marked()
@@ -27,6 +28,7 @@ const marked = new Marked()
         level: "container",
       },
       iconDirective,
+      cmdDirective,
     ]),
     {
       extensions: [...markedColumns()],