cinny: load Element Call from call.chat.lotusguild.org (cinny #43)

Sets elementCallUrl so the web app frames the call page on its own origin
(desktop keeps its bundled copy). Applied on LXC 106 in place (the live file
also carries the injected gifApiKey; backup in /root/config-backups/), since
the matrix-deploy webhook there has not fired since May.

Rollback: remove this key (live: restore the backup) and new calls use the
bundled same-origin page again.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01PPmy3tPq869XDW4njjVaKA

cinny/config.json

@@ -16,5 +16,6 @@
     "enabled": false,
     "basename": "/"
   },
-  "gifApiKey": ""
-}
+  "gifApiKey": "",
+  "elementCallUrl": "https://call.chat.lotusguild.org/public/element-call/index.html"
+}