Mouse scroll not working in MobaXterm/PuTTY SSH sessions (alt-screen mode)

## Environment
- **Copilot CLI version**: 1.0.32
- **Terminal**: MobaXterm (SSH session to Linux host)
- **TERM**: xterm-color
- **OS**: RHEL/CentOS (remote host)

## Problem

Mouse scroll does not work for browsing conversation history in the Copilot CLI session when connected via MobaXterm (SSH). The terminal supports mouse events correctly — scroll and paste work fine in the normal bash shell. The issue is specific to the Copilot CLI's alt-screen TUI.

## Current behavior

| Config setting | Scroll | Paste |
|---|---|---|
| `"mouse": true` | ❌ Not working | ❌ Broken (corrupted text) |
| `"mouse": false` | ❌ Not working | ✅ Works |

Only PgUp/PgDn keys work for scrolling conversation history.

## Expected behavior

With `"mouse": true`, mouse wheel scroll should navigate the conversation history within the CLI's alt-screen buffer, similar to how it works in other TUI applications (e.g., less, vim).

## Notes

- The changelog for v1.0.14 mentions "Pasted text is no longer corrupted when mouse support is active" — this fix does not appear to work with MobaXterm/PuTTY terminals.
- The terminal correctly supports SGR mouse encoding (`\e[?1006h` succeeds).
- Normal terminal scrollback works fine outside the Copilot CLI session.
- This was reportedly working ~1 month ago (around v1.0.7 timeframe) before a subsequent update broke it.

## Workaround

Keep `"mouse": false` in `~/.copilot/config.json` and use PgUp/PgDn for scrolling.

Reproduce the issue in a MobaXterm or PuTTY SSH session on a Linux host with TERM=xterm-color, testing both mouse settings and the alt-screen TUI. Start by tracing mouse-event handling and compare behavior with the v1.0.7 timeframe and the v1.0.14 paste fix. Done means mouse scrolling navigates conversation history without corrupting pasted text, while PgUp/PgDn remains functional.

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