docs(declare): document the YAML declare format

Update the journal-set doc entry, the CLI diagnostic table, and the
authoring skill, along with the in-app empty-state hint and the var
message comment.

src/components/journal/VariableView.tsx

@@ -53,7 +53,7 @@ export const VariableView: Component = () => {
         when={hasAnyData()}
         fallback={
           <p class="text-center text-gray-400 text-xs py-8">
-            暂无变量定义。在文档中使用 ```csv role=declare 代码块定义变量。
+            暂无变量定义。在文档中使用 ```yaml role=declare 代码块定义变量。
           </p>
         }
       >

src/components/journal/types/var.tsx

@@ -4,7 +4,7 @@
  * Emitters: gm, player
  * Command: /set $key expression
  *
- * Variable declarations and tag modifiers are authored in ```csv role=declare
+ * Variable declarations and tag modifiers are authored in ```yaml role=declare
  * code blocks in markdown documents. The stream carries `set` mutations that
  * build up the runtime variable store additively.
  */