Add deep links for skills and Automations

### Feature summary
Add reviewed deep-link flows for skills and Automations.

### What problem are you trying to solve?
Other apps and websites cannot open GitHub Copilot with a skill ready to add or a prefilled Automation ready to configure.

### Proposed solution
Support deep links that open GitHub Copilot with:

1. A skill ready to add from a supported source.
2. A prefilled Automation containing its name, prompt, schedule, and project.

Both flows must require user review and confirmation before making changes, consistent with existing prompt and plugin deep links.

### Workflow impact
This lets external apps and websites hand off skill installation and Automation setup without bypassing user control.

### Installation context
N/A

### Additional context
Follow the review-and-confirm interaction used by existing prompt and plugin deep links.

まず、issue で参照されている既存の prompt および plugin のディープリンクフローを追跡します。skill リンクと Automation リンクの入力を定義し、両方がレビュー済みで事前入力されたフローを開き、変更を行う前に確認を必要とすることを検証します。

索引モデルが issue の本文から書いたものです。