Esc in /tasks overlay also dismisses active question prompt

### Describe the bug

When the Copilot CLI `/tasks` overlay is open and the agent asks a question, pressing `Esc` to close the task/subagent menu also affects the underlying question prompt.

The same `Esc` keypress appears to be handled twice:

1. It closes the `/tasks` overlay.
2. It also dismisses or skips the active question prompt underneath.

This prevents the user from answering the question and can cause the agent to continue with an unintended skipped/default response.

This seems inconsistent with the documented `Esc` behavior for Copilot CLI, where an open dialog, overlay, or picker should be closed before `Esc` acts as a broader cancel action.

References:

- [`/tasks` command reference](https://docs.github.com/en/copilot/reference/copilot-cli-reference/cli-command-reference)
- [`Esc` behavior in Copilot CLI](https://docs.github.com/en/copilot/concepts/agents/copilot-cli/cancel-and-roll-back)
- [`/fleet` and subagent task execution](https://docs.github.com/en/copilot/concepts/agents/copilot-cli/fleet)

### Affected version

GitHub Copilot CLI 1.0.49.

### Steps to reproduce the behavior

1. Start an interactive Copilot CLI session.
2. Start a task that uses subagents or background tasks.
3. Open the task/subagent manager with `/tasks`.
4. While the `/tasks` overlay is open, wait for the agent to ask a question or clarification.
5. Press `Esc` once, intending only to close the `/tasks` overlay.
6. Observe that the active question is also skipped or dismissed.

### Expected behavior

Pressing `Esc` while the `/tasks` overlay is open should only close that overlay and return focus to the active question prompt.

The question should remain visible and answerable.

### Additional context

This looks like a key handling or focus propagation issue. The `/tasks` overlay appears not to consume the `Esc` event after using it to close itself, so the same keypress reaches the global cancel handler or the underlying question UI.

A possible fix would be to make the `/tasks` overlay treat `Esc` as handled when it closes the overlay, preventing the key event from being forwarded to lower-priority UI layers.

A regression test could cover this stacked UI case:

1. An active question prompt is visible underneath the `/tasks` overlay.
2. The user presses `Esc` once.
3. Only the `/tasks` overlay closes.
4. The question prompt remains open and answerable.

Reproduce the stacked UI case by opening the /tasks overlay while a question prompt is active, then pressing Esc once. Trace Esc handling from the /tasks overlay to the underlying question prompt and add a regression test covering that sequence. Done means the overlay closes while the question remains visible and answerable.

索引モデルが issue の本文から書いたものです。