Edit file diff panel covers previous assistant output, blocking review before approval

### Describe the bug

When Copilot proposes a file edit with a large diff (many added/removed lines), the "Edit file" diff panel expands to fill most of the terminal screen. This pushes the assistant's preceding explanation — reasoning, analysis, context — entirely off-screen or out of the visible viewport.

As a result, the user must decide whether to approve or reject the edit **without being able to see what the assistant just said**, since scrolling is not possible while the interactive confirmation prompt is active.

### Steps to reproduce

1. Ask Copilot to make a large change to a file (e.g. adding 50+ lines).
2. Copilot outputs an explanation, then shows the "Edit file" confirmation prompt with a large diff.
3. The diff panel occupies most or all of the terminal, pushing the assistant's explanation out of view.
4. The user cannot scroll up to read the previous output while the confirmation prompt is active.

### Expected behavior

The assistant's output that immediately preceded the "Edit file" prompt should remain visible (or at least accessible) while the user is deciding whether to approve. For example:
- The diff panel could be scrollable within a fixed-height region, or
- The diff could be collapsed/truncated by default with an option to expand, or
- The assistant's last message could be shown above the diff in a pinned/summary area.

### Affected version

GitHub Copilot CLI 1.0.41

### Additional context

This is especially problematic when Copilot's explanation is the key reasoning the user needs to evaluate whether to approve the edit. Being forced to approve blindly — just to then scroll up and read the explanation — breaks the review flow.

Reproduzieren Sie das Problem in GitHub Copilot CLI 1.0.41, indem Sie die Bearbeitung einer großen Datei anfordern, und beobachten Sie anschließend die interaktive Eingabeaufforderung "Edit file" mit dem Diff. Prüfen Sie die Bestätigung im Terminal und das Verhalten des Diff-Panels und berücksichtigen Sie die im Issue vorgeschlagenen Ansätze; als erledigt gilt die Aufgabe, wenn die vorangegangene Erklärung des Assistenten sichtbar oder zugänglich bleibt, während die Genehmigung aussteht.

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