feat(content): add draft support for content collections

This commit introduces a draft system for the 'events' and 'news' collections. A `draft` boolean field has been added to the content schema, and frontend queries are now updated to only fetch and
display content where `draft` is `false`. This allows content to be created and saved without being publicly visible, improving the publishing workflow.

app/pages/events/index.vue

@@ -12,7 +12,11 @@
 import type { ChangelogVersionProps } from "@nuxt/ui";
 
 const { data: events } = await useAsyncData("events", () =>
-  queryCollection("events").order("date", "DESC").limit(3).all()
+  queryCollection("events")
+    .where("draft", "=", false)
+    .order("date", "DESC")
+    .limit(3)
+    .all()
 );
 
 // 将 news 数据转换成 UBlogPosts 可用格式