Home/End in ask_user answer input also scroll the timeline to top/bottom #5113

Describe the bug

While the agent is asking a question (ask_user / "Asking user"), pressing Home or End
inside the answer input moves the input cursor and also scrolls the conversation
timeline to the very top / bottom.

The Home/End scroll shortcut (added in v1.0.52, see #3470) is meant to fire only when
the text cursor is already at the start/end of the prompt. However, the check seems to
look at the main chat prompt rather than the input that currently has focus. While the
question dialog is open, the main prompt is usually empty, so its cursor counts as being
at both the start and the end. As a result, every Home/End press inside the dialog
triggers the scroll.

Ctrl+A / Ctrl+E inside the dialog move the cursor without scrolling, as expected.

Affected version

GitHub Copilot CLI 1.0.95.

Steps to reproduce the behavior

1. Start an interactive session (alt-screen mode) with enough history to make the timeline scrollable.
2. Ask the agent something that makes it call ask_user with a free-form answer.
3. Type a few words in the answer field, move the cursor to the middle, then press Home.
4. The cursor jumps to the start of the answer, and the timeline also jumps to the top.
   End behaves the same way: the timeline jumps to the bottom.

Expected behavior

While the question dialog has focus, Home/End should only move the cursor in the dialog's
input. Either scroll only when the dialog's own cursor is already at the start/end, or
turn off the timeline Home/End scrolling while the dialog is open.

Additional context

• The normal chat prompt works as documented: the first Home moves the cursor, and the
  second Home scrolls.
• OS: Linux (WSL2 on Windows 11)
• CPU architecture: x86_64
• Terminal emulator: WezTerm (Windows) → WSL → herdr 0.9.1 (terminal multiplexer).
  herdr forwards a single ESC [ H per Home press.
• Shell: fish