Add a way to list currently running Copilot CLI sessions with their status

Feature request: Anthropic's Claude Code CLI has a ⁠claude agents --json⁠ command that lists every currently-running interactive session on the machine, each with an id, name, cwd, and status (idle/busy/waiting/blocked). This makes it possible to build an external dashboard/monitor across multiple parallel sessions (e.g. several terminal tabs or IDE panes each running their own session).
Copilot CLI has no equivalent today — ⁠--resume⁠/⁠--session-id⁠/⁠/session⁠ all operate on a specific known session for resuming, not on discovering other currently-active sessions and their live state. The closest thing is the undocumented ⁠~/.copilot/session-state//events.jsonl⁠ per-session event log, but it's internal, unversioned, and provides no "is this session still alive" signal (no PID recorded anywhere).
Ask: a ⁠copilot sessions --json⁠ (or similar) command/flag that lists currently-active sessions with at least an id, working directory, and a coarse status (busy/idle, and ideally "waiting for tool permission" as a third state) — enabling external tooling to build a multi-session status dashboard the same way it's possible for Claude Code today.

まず、既存のセッション制御（--resume、--session-id、/session）と、issue で説明されている未ドキュメントの ~/.copilot/session-state//events.jsonl ログを調べます。アクティブなセッションとそのライブ状態をどのように特定できるかを判断し、そのうえで、各アクティブセッションの id、作業ディレクトリ、概要ステータスを報告する JSON リストを完成条件として定義します。