Feature request: configurable scroll speed / scroll-sensitivity setting for the Copilot CLI TUI

### Describe the feature or problem you'd like to solve

**Problem:** When running Copilot CLI inside the VS Code integrated terminal, mouse-wheel/trackpad scrolling in the Copilot session is dramatically faster than scrolling in a normal terminal shell. Each physical trackpad gesture jumps many lines at once, making it very hard to read back through the conversation or review output. Scrolling in the same terminal *outside* a Copilot session behaves normally and controllably.

### Proposed solution

**Root cause (as I understand it):** Copilot CLI runs as a full-screen TUI using the alternate screen buffer with application mouse tracking enabled. This bypasses the terminal's native scrollback, so VS Code's own scroll pacing no longer applies, and Copilot handles wheel events itself — amplifying each tick into many lines.

**Why existing workarounds don't work for me:**
- **`Shift+scroll`** — does not help; scrolling is still too fast.
- **`terminal.integrated.mouseWheelScrollSensitivity`** — I already have this set to `0.3`, and it has no effect on the Copilot session (it only affects the terminal's native scrollback, which Copilot bypasses). If anything it confirms the setting is out of the path, since Copilot still scrolls fast despite the low value.
- **Lowering OS/trackpad scroll speed** — this is system-wide and would slow scrolling in every app (browser, editor, Finder, etc.). I don't want to degrade my whole system just to fix one tool.
- **In-app navigation (`ctrl+o`, `/search`, `/context`)** — not a substitute. I rely on my laptop trackpad/scroll for reading and navigating, and keyboard/command navigation doesn't fit my workflow.

**Request:** Please add a Copilot-side scroll-speed / scroll-sensitivity setting (e.g., lines-per-tick or a multiplier) so trackpad/mouse scrolling in the CLI TUI can be tuned without changing system-wide OS settings. A sensible default that matches normal terminal scroll pacing would also help.

**Environment:** Copilot CLI v1.0.68, macOS, running inside the VS Code integrated terminal, trackpad scrolling.

### Example prompts or workflows

N/A

### Additional context

N/A

The issue names no files, tests, or implementation entry points. Start by locating the Copilot CLI TUI's application mouse-tracking and wheel-event handling, then determine how a configurable sensitivity setting could be exposed and verified without changing native terminal scrollback behavior.

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