Poll for new inbox messages every 30 seconds in admin

Silently checks for new contact submissions in the background and
prepends any new ones to the inbox without disrupting the current view.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

src/AdminPage.tsx

@@ -1427,6 +1427,24 @@ export default function AdminPage({ content, onSave, onLogout }: Props) {
     setContactStatus('ready')
   }
 
+  // Poll for new messages every 30 seconds — only prepend genuinely new ones
+  useEffect(() => {
+    const interval = setInterval(async () => {
+      try {
+        const r = await fetch('/api/admin-contact-submissions')
+        if (!r.ok) return
+        const data = await r.json() as { submissions?: ContactSubmission[] }
+        const fresh = Array.isArray(data.submissions) ? data.submissions : []
+        setContactSubmissions(prev => {
+          const existingIds = new Set(prev.map(s => s.id))
+          const newOnes = fresh.filter(s => !existingIds.has(s.id))
+          return newOnes.length > 0 ? [...newOnes, ...prev] : prev
+        })
+      } catch { /* silent — don't disrupt the UI */ }
+    }, 30_000)
+    return () => clearInterval(interval)
+  }, [])
+
   useEffect(() => {
     const visible = contactSubmissions.filter(item => (emailMailboxView === 'archived' ? item.archived === true : item.archived !== true))
     if (visible.length === 0) {