feat(web): mod+alt+enter on an existing thread sends and opens a new thread - #15050

This check requires the following CI step(s) to complete first, but they did not appear on this commit within 1m0s of this check starting:

• Check

Verify the requires field in your .macroscope/*.md front matter matches the exact check run name as it appears on GitHub. If the step is real but published late — a conditional job, or a workflow queued while a previous run is still cancelling — raise waitsForDiscoveryTimeout (minutes) to give it longer to appear. The cost of a longer window is that a step which never appears at all takes that long to skip.