Change banner to maintenance notice

Author: ksen0

src/content/banner/en.mdx

@@ -1,8 +1,7 @@
 ---
 # Give each new message a unique title so we know which one a user closed
-title: "beta-site"
-link: "https://beta.p5js.org"
+title: "maintenance-20260322"
 hidden: false
 ---
 
-Looking for the new version? Find p5.js 2.0 here!
+This website will be undergoing scheduled maintenance on Sunday March 22, 2026 8:00am CET, and may be down for up to 24 hours.