High priority: bare left/right arrow hijacks cursor key for session navigation, discarding in-progress input (data loss)

## Summary (high priority — causes data loss)

In the interactive CLI, the **bare left/right arrow keys are overloaded for session navigation**. Specifically:

- **Left arrow** opens the Sessions sidebar.
- A **second left arrow within ~70–450 ms** starts a **new session** (a double-tap gesture; the timing window is hardcoded).
- **Right arrow** jumps to the Agents tab.

This overloads the single most fundamental cursor key in any text field, and — most importantly — **it silently discards in-progress input** (a correction/follow-up I was composing), with no confirmation and no auto-stash.

## Core principle: bare arrow keys should not be app keybindings in a CLI

Binding **bare (unmodified) arrow keys to application actions is a fundamental anti-pattern for a terminal/CLI program.** In a text interface the arrow keys have exactly one universally understood job — move the cursor. Users rely on that contract from every shell, REPL, and terminal editor. Any application-level navigation (sidebars, tabs, session switching, new session) should be bound to a modifier or leader chord (e.g. `ctrl+…`, or the existing `ctrl+x → …` pattern), never to a naked arrow key. Overloading bare arrows — especially with a destructive action — guarantees accidental, muscle-memory-driven mistakes.

## Why this is high priority

- **Data loss:** while composing a correction or follow-up (often while the agent is working), reaching for the arrow key out of habit triggers navigation / a new session and **destroys the correction I was in the middle of writing**. Silent loss of user input to a stray cursor keypress is a serious defect, not a cosmetic one.
- **Violates universal expectations:** left/right arrows mean "move the cursor" in every shell, editor, and text field. Overloading them — especially with a *destructive* double-tap gesture — breaks muscle memory everyone has.
- **No escape hatch:** there is no setting to disable or rebind this in `/settings` or `settings.json`, and the binding is not listed in the public keyboard-shortcut help. It's effectively hidden and unavoidable.

## Steps to reproduce

1. Start `copilot` (interactive).
2. Press **Left** (for example while composing or correcting a prompt, or while the agent is working).
- The Sessions sidebar opens.
3. Press **Left** again quickly (within ~70–450 ms).
- A **new session** is started and any in-progress prompt/correction is discarded.

> Note: the exact conditions under which a bare arrow is captured for navigation vs. cursor movement are not documented; the observed effect is that a correction in progress can be lost.

## Expected behavior

- Bare left/right arrows should only move the cursor. They should never trigger navigation or start a new session.
- In-progress input must never be discarded without confirmation or an automatic stash.

## Suggested fixes (any one resolves it)

1. Don't bind bare left/right to navigation — require a modifier or leader chord (e.g. `ctrl+x → …`, consistent with the existing `ctrl+x → h` to hide the sidebar).
2. Add a setting to disable arrow-key session navigation.
3. Never discard in-progress input without confirmation or auto-stash.
4. At minimum, remove the destructive double-tap-left → new-session binding.

## Environment

- Copilot CLI: **1.0.71-3**
- OS: **Windows**

Bắt đầu bằng cách tái hiện hành vi trong CLI tương tác trên Windows, sử dụng các bước với phím mũi tên trái và thao tác nhấn đúp được liệt kê trong khi soạn input. Xem lại các phím tắt và các khu vực cài đặt được tham chiếu trong `/settings` và `settings.json`; được xem là hoàn tất khi các phím mũi tên không kèm phím bổ trợ di chuyển con trỏ và không có input đang nhập dở bị loại bỏ trong quá trình điều hướng.

Do mô hình lập chỉ mục viết ra từ nội dung của issue.