feat(markdown): support yaml role=tag info string

Accept yaml role=tag alongside legacy yaml/tag so the block
body gets yaml syntax highlighting, matching the CLI role=
attribute convention. Copy button now emits the role=tag form.

content/deck-test.md

@@ -15,3 +15,26 @@ bleed: 1
 padding: 2
 layers: name1:1,1-2,2f12 name2:4,7-5,8f12s num1:1,3-2,4f12 num2:4,5-5,6f12s
 ```
+
+## 使用 yaml role=tag 语法创建 md-deck（推荐，可语法高亮）
+
+```yaml role=tag
+tag: md-deck
+body: ./names.csv
+data-config:
+  size: 54x86
+  grid: 5x8
+  layers:
+    - prop: name1
+      pos: 1,1-2,2
+      font: 12
+    - prop: num2
+      pos: 4,5-5,6
+      font: 12
+      orientation: s
+    - template: |
+        **{{name1}}** / {{num1}}
+      pos: 1,3-5,4
+      font: 6
+      align: l
+```