Scheduling or automated triggering of skills

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

Allow scheduling or triggering of repeatable skills

### Proposed solution

Add first-class support for scheduling skills to run on a recurring cadence, with built-in configuration and notification capabilities:

1. **Schedule configuration via `/skills` or a new `/schedule` command** — Allow users to attach a recurrence rule (e.g., cron expression, or simple presets like `daily`, `weekly on Monday at 9am`) to any installed skill.

2. **Background daemon or system integration** — A lightweight background service (or integration with OS schedulers) that triggers skill execution at the configured times without requiring the user to have the CLI open.

3. **Notification and approval flow** — When a scheduled skill runs, notify the user (e.g., via system notification, or a summary shown on next CLI launch) and, for skills that require approval before taking action, queue the results for user review rather than executing autonomously.

4. **Schedule management** — Commands to list, pause, resume, and delete scheduled skills:
- `/schedule list` — View all active schedules
- `/schedule pause ` — Temporarily pause a schedule
- `/schedule delete ` — Remove a schedule
- `/schedule history ` — View past execution results

### Example prompts or workflows

### Setting up a schedule

```
> /schedule add workiq --every friday --prompt "Summarize my week — key emails, decisions, and open items"
✔ Scheduled "workiq" to run every Friday with the provided prompt
```

### Viewing and managing schedules

```
> /schedule list

Skill Schedule Next Run Status
example-approvals Every Monday 9:00 AM 2026-03-02 09:00 Active
workiq Every Friday 5:00 PM 2026-02-27 17:00 Active

> /schedule pause example-approvals
✔ Paused "example-approvals" schedule

> /schedule history workiq
Run Date Status Summary
2026-02-20 17:00 Completed Summarized 42 emails, 8 meetings
2026-02-13 17:00 Completed Summarized 31 emails, 5 meetings
```

### Notification on next CLI launch

```
$ copilot

📋 Scheduled skill results available:
• example-approvals (ran Mon Feb 23 at 9:00 AM) — 12 entries ready for review
Run "/schedule review example-approvals" to review and approve

>
```

### Additional context

_No response_

該 issue 未指出實作檔案、測試或進入點；首先定位現有的 skill 和 CLI 指令架構。定義排程設定、背景觸發、通知與核准處理，以及管理和歷史指令，然後端到端驗證重複執行和審查流程。

由索引模型根據 Issue 內容生成。