fix: app_exit keybind ignored when using <leader> (including default <leader>q)

[razor-x]

Fixes#3851

What does this PR do?

Summary

• Add a global app_exit handler so leader key combos reach exit even when prompt focus is blurred, while still respecting the “only exit when prompt is empty” rule in packages/opencode/src/cli/cmd/tui/app.tsx:183.
  Why this fixes it
• q was being consumed while the prompt was blurred by leader mode, so the prompt-level app_exit handler never ran. The new global handler uses useKeyboard and usePromptRef to exit consistently.

How did you verify your code works?

Built and ran locally, verified q exits the app as expected.

I was not able to find a way to add an test for this. The core issue depends on the app.tsx running and focus passing between the prompt an the app, so a unit test is mostly ceremonial. An e2e test would require a net test harness to mount the TUI app similar to how playwright e2e works.

[github-actions]

Thanks for your contribution!

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Please:

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[github-actions]

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No duplicate PRs found

[rekram1-node]

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