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.

首先，跟踪 issue 中引用的现有 prompt 和 plugin 深层链接流程。定义 skill 和 Automation 链接输入，然后验证两者都会打开一个经过审核且预填充的流程，并在进行更改前要求确认。

由索引模型根据 Issue 内容生成。