Harden embed live refresh with reconnect backoff and poll fallback.

Document Nginx SSE proxy settings for long-lived live streams.

Co-authored-by: Cursor <cursoragent@cursor.com>

lib/instance/templates/embed_shell.html

@@ -145,7 +145,7 @@ const ORDER_ENTRY_MODEL_CODE_TO_CATEGORY = {{ entry_model_code_to_category | toj
 window.__INSTANCE_DISPLAY__ = {{ display | tojson }};
 </script>
 <script src="/static/instance_settings_prefs.js?v=21"></script>
-<script src="/static/instance_live.js?v=6"></script>
+<script src="/static/instance_live.js?v=7"></script>
 <script src="/static/instance_embed.js?v=31"></script>
 <script src="/static/instance_mobile_nav.js?v=2"></script>
 </body>