New-thread shortcuts only work when the prompt composer is focused #1812

Summary

On Linux BB Desktop 0.38.0, the new-thread shortcuts only work while the prompt composer has focus.

Steps to reproduce

1. Open a project thread.
2. Click the project bar, sidebar, or timeline so the prompt box is no longer focused.
3. Press Ctrl+N or Ctrl+Shift+O.
4. Nothing happens.
5. Click inside the prompt composer and press either shortcut again.
6. The new-thread composer opens.

Expected behavior

Both new-thread shortcuts should work across BB's main surface, regardless of whether the project bar, sidebar, timeline, or prompt composer currently has focus.

Notes

The effective keybindings report thread.new with the mainSurface context and only exclude modalOpen, so the observed composer-only behavior appears narrower than the declared context.

Environment: Linux, BB Desktop 0.38.0.

AGENT GENERATED: by GPT-5.6 Sol