fix(preview): restore truncated HTML closing tags

The _patch.cjs script accidentally stripped </script></body></html>
when replacing the WebSocket section, causing the inline JavaScript
to never terminate — the browser parsed everything as script content
and all functions were undefined.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

preview/index.html

@@ -358,4 +358,6 @@ showMessage('Gmail / Outlook simulation is approximate. For accurate rendering w
     showMessage('Dev server connection failed', 'error');
   };
 })();
-
+</script>
+</body>
+</html>