fix: hide changelog banner when messages are present

Fix issue where changelog banner remained visible after messages were sent.
Apply the same logic as beta badge to hide when messages exist.

Changes:
- Add messages-changed event listener to ChangelogBanner
- Hide banner when hasMessages is true
- Maintain consistency with BetaBadge behavior

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude <noreply@anthropic.com>

Author: miurla

components/changelog-banner.tsx

@@ -1,5 +1,7 @@
 'use client'
 
+import { useEffect, useState } from 'react'
+
 import { X } from 'lucide-react'
 
 import { useChangelog } from '@/hooks/use-changelog'
@@ -8,8 +10,21 @@ import { IconLogo } from '@/components/ui/icons'
 
 export function ChangelogBanner() {
   const { changelog, isVisible, dismiss } = useChangelog()
+  const [hasMessages, setHasMessages] = useState(false)
+
+  useEffect(() => {
+    const handleMessagesChanged = (e: Event) => {
+      const customEvent = e as CustomEvent<{ hasMessages: boolean }>
+      setHasMessages(customEvent.detail.hasMessages)
+    }
+
+    window.addEventListener('messages-changed', handleMessagesChanged)
+    return () =>
+      window.removeEventListener('messages-changed', handleMessagesChanged)
+  }, [])
 
-  if (!isVisible || !changelog) return null
+  // Don't show if there are messages or if not visible
+  if (!isVisible || !changelog || hasMessages) return null
 
   return (
     <div className="fixed bottom-4 right-4 z-40 animate-in slide-in-from-bottom-5 duration-300">