feat: add announcements feature with JSON data and interactive UI

- Created a new JSON file for announcements containing activity and maintenance updates.
- Implemented a JavaScript module to fetch, filter, and display announcements dynamically.
- Added functionality for editing announcements with a modal interface and live preview.
- Included drag-and-drop support for content blocks within the announcement editor.
- Enhanced user experience with category filtering and search capabilities.

js/components.js

@@ -15,6 +15,7 @@ const Components = {
                 <a href="/doc.html">文档</a>
                 <a href="/map.html">地图</a>
                 <a href="/facilities.html">设施</a>
+                <a href="/announcements.html">公告</a>
                 <a href="/photo.html">相册</a>
                 <a href="/stats.html">数据</a>
                 <a href="/sponsor.html">赞助</a>
@@ -32,6 +33,7 @@ const Components = {
             <a href="/doc.html">文档</a>
             <a href="/map.html">地图</a>
             <a href="/facilities.html">设施</a>
+            <a href="/announcements.html">公告</a>
             <a href="/photo.html">相册</a>
             <a href="/stats.html">数据</a>
             <a href="/sponsor.html">赞助</a>