fix preview not updating

Made-with: Cursor

src/App.tsx

@@ -50,6 +50,9 @@ export default function App() {
     if (!template) return
 
     let cancelled = false
+    // Clear previous output immediately so the iframe can't appear "stuck".
+    setHtml('')
+    setText('')
     const handle = setTimeout(async () => {
       setLoading(true)
       setError(null)
@@ -73,7 +76,7 @@ export default function App() {
       cancelled = true
       clearTimeout(handle)
     }
-  }, [brand, templateId, data])
+  }, [brand, template, data])
 
   const styles = {
     page: {