Each widget in the Widgets panel (and the open widget's header) gets an
"Open in a new window" button, so a pad or board can sit beside the chat.
It opens the same filled-in URL the frame uses (widgetCompleteUrl, now
shared) with noopener,noreferrer, standalone as in Element. Only
cross-origin https URLs get the button: room state can carry anything,
e.g. a script URL from another client.
Refs #205
Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_017PCb59uY3UKqDqt7B6hzd5