docs(doc-entries): Show examples as code blocks

Directive examples sat bare in the doc bodies, so rendering them as
markdown executed the directives: live components, missing-file
fetches, and style side effects on the dialog. Wrap each example in
a markdown fence, matching the convention already used by md-table.

src/doc-entries/md-dice.md

@@ -8,11 +8,20 @@ title: 骰子组件
 
 **语法：** `:md-dice[公式]{key="标识"}`
 
-**攻击检定：** :md-dice[1d20+5]{key="attack"}
+**攻击检定：**
+```markdown
+:md-dice[1d20+5]{key="attack"}
+```
 
-**伤害掷骰：** :md-dice[2d6+3]{key="damage"}
+**伤害掷骰：**
+```markdown
+:md-dice[2d6+3]{key="damage"}
+```
 
-**优势检定：** :md-dice[2d20k1+5]{key="advantage"}
+**优势检定：**
+```markdown
+:md-dice[2d20k1+5]{key="advantage"}
+```
 
 点击 🎲 图标执行投掷，显示结果；点击文字重置为原始公式。